selftests/bpf: Fix s390x vmlinux path

After commit edd4a86 ("s390/boot: get rid of startup archive")
there is no more compressed/ subdirectory.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20230129190501.1624747-8-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: iii-i

tools/testing/selftests/bpf/vmtest.sh

@@ -13,7 +13,7 @@ s390x)
 	QEMU_BINARY=qemu-system-s390x
 	QEMU_CONSOLE="ttyS1"
 	QEMU_FLAGS=(-smp 2)
-	BZIMAGE="arch/s390/boot/compressed/vmlinux"
+	BZIMAGE="arch/s390/boot/vmlinux"
 	;;
 x86_64)
 	QEMU_BINARY=qemu-system-x86_64