kernel: fix build errors for clang

[binarycraft007]

This PR fixes some compile error for clang when I was trying to cross compile kpimg.

KernelPatch/kernel/include/cache.h:48:45: error: value size does not match register size specified by the constraint and modifier
    asm volatile("mrs %0, CurrentEL" : "=r"(el));
                                            ^
KernelPatch/kernel/patch/module/module.c:13:10: note: in file included from KernelPatch/kernel/patch/module/module.c:13:
#include <cache.h>
         ^
KernelPatch/kernel/include/cache.h:48:23: note: use constraint modifier "w"
    asm volatile("mrs %0, CurrentEL" : "=r"(el));
                      ^~~
KernelPatch/kernel/linux/include/linux/rcupdate.h:81:1: error: non-void function does not return a value in all control paths
}
^
KernelPatch/kernel/patch/module/module.c:23:10: note: in file included from KernelPatch/kernel/patch/module/module.c:23:
#include <linux/rcupdate.h>
         ^
KernelPatch/kernel/linux/include/linux/rcupdate.h:139:1: error: non-void function does not return a value in all control paths
}
^
KernelPatch/kernel/patch/module/module.c:23:10: note: in file included from KernelPatch/kernel/patch/module/module.c:23:
#include <linux/rcupdate.h>
         ^
KernelPatch/kernel/linux/include/linux/rcupdate.h:143:1: error: non-void function does not return a value in all control paths
}
^
KernelPatch/kernel/patch/module/module.c:23:10: note: in file included from KernelPatch/kernel/patch/module/module.c:23:
#include <linux/rcupdate.h>
         ^
KernelPatch/kernel/linux/include/linux/rcupdate.h:147:1: error: non-void function does not return a value in all control paths
}
^
KernelPatch/kernel/patch/module/module.c:23:10: note: in file included from KernelPatch/kernel/patch/module/module.c:23:
#include <linux/rcupdate.h>
         ^
KernelPatch/kernel/linux/include/linux/rcupdate.h:151:1: error: non-void function does not return a value in all control paths
}
^
KernelPatch/kernel/patch/module/module.c:23:10: note: in file included from KernelPatch/kernel/patch/module/module.c:23:
#include <linux/rcupdate.h>
         ^
KernelPatch/kernel/linux/include/linux/rcupdate.h:160:1: error: non-void function does not return a value in all control paths
}
^
KernelPatch/kernel/patch/module/module.c:23:10: note: in file included from KernelPatch/kernel/patch/module/module.c:23:
#include <linux/rcupdate.h>
         ^
KernelPatch/kernel/linux/include/linux/rcupdate.h:164:1: error: non-void function does not return a value in all control paths
}
^
KernelPatch/kernel/patch/module/module.c:23:10: note: in file included from KernelPatch/kernel/patch/module/module.c:23:
#include <linux/rcupdate.h>
         ^
KernelPatch/kernel/patch/module/module.c:189:13: error: expected expression
            unsigned long addr = symbol_lookup_name(name);
            ^
KernelPatch/kernel/patch/module/module.c:192:18: error: use of undeclared identifier 'addr'
            if (!addr) {
                 ^
KernelPatch/kernel/patch/module/module.c:197:31: error: use of undeclared identifier 'addr'
            sym[i].st_value = addr;
                              ^

[bmax121]

have you tested the kpimg

[binarycraft007]

have you tested the kpimg

patch was successful, os is enable to boot, but the latest apatch version is too old maybe, it doesn't detect kpimg with superkey inputed.

[binarycraft007]

have you tested the kpimg

hi, just installed the latest apk from apatch github workflow, the kpimg works

[bmax121]

good, but your modification is no longer applicable to gcc

[sekaiacg]

Can kpm be successfully loaded after using clang to compile kpimg?
I used clang and found that module loading failed.