zfs_get_enclosure_sysfs_path(): don't leak dev path

Also always free tmp2 at the end

Before:
nabijaczleweli@tarta:~/uwu$ valgrind --leak-check=full ./blergh
==8947== Memcheck, a memory error detector
==8947== Using Valgrind-3.14.0 and LibVEX
==8947== Command: ./blergh
==8947==
(null)
==8947==
==8947== HEAP SUMMARY:
==8947==     in use at exit: 23 bytes in 1 blocks
==8947==   total heap usage: 3 allocs, 2 frees, 1,147 bytes allocated
==8947==
==8947== 23 bytes in 1 blocks are definitely lost in loss record 1 of 1
==8947==    at 0x483577F: malloc (vg_replace_malloc.c:299)
==8947==    by 0x48D74B7: vasprintf (vasprintf.c:73)
==8947==    by 0x48B7833: asprintf (asprintf.c:35)
==8947==    by 0x401258: zfs_get_enclosure_sysfs_path
                         (zutil_device_path_os.c:191)
==8947==    by 0x401482: main (blergh.c:107)
==8947==
==8947== LEAK SUMMARY:
==8947==    definitely lost: 23 bytes in 1 blocks
==8947==    indirectly lost: 0 bytes in 0 blocks
==8947==      possibly lost: 0 bytes in 0 blocks
==8947==    still reachable: 0 bytes in 0 blocks
==8947==         suppressed: 0 bytes in 0 blocks
==8947==
==8947== For counts of detected and suppressed errors, rerun with: -v
==8947== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

nabijaczleweli@tarta:~/uwu$ sed -n 191p zutil_device_path_os.c
        tmpsize = asprintf(&tmp1, "/sys/block/%s/device", dev_name);

After:
nabijaczleweli@tarta:~/uwu$ valgrind --leak-check=full ./blergh
==9512== Memcheck, a memory error detector
==9512== Using Valgrind-3.14.0 and LibVEX
==9512== Command: ./blergh
==9512==
(null)
==9512==
==9512== HEAP SUMMARY:
==9512==     in use at exit: 0 bytes in 0 blocks
==9512==   total heap usage: 3 allocs, 3 frees, 1,147 bytes allocated
==9512==
==9512== All heap blocks were freed -- no leaks are possible
==9512==
==9512== For counts of detected and suppressed errors, rerun with: -v
==9512== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes openzfs#11993

lib/libzutil/os/linux/zutil_device_path_os.c

@@ -195,10 +195,8 @@ zfs_get_enclosure_sysfs_path(const char *dev_name)
 	}
 
 	dp = opendir(tmp1);
-	if (dp == NULL) {
-		tmp1 = NULL;	/* To make free() at the end a NOP */
+	if (dp == NULL)
 		goto end;
-	}
 
 	/*
 	 * Look though all sysfs entries in /sys/block/<dev>/device for
@@ -216,11 +214,8 @@ zfs_get_enclosure_sysfs_path(const char *dev_name)
 		size = readlink(tmp2, buf, sizeof (buf));
 
 		/* Did readlink fail or crop the link name? */
-		if (size == -1 || size >= sizeof (buf)) {
-			free(tmp2);
-			tmp2 = NULL;	/* To make free() at the end a NOP */
+		if (size == -1 || size >= sizeof (buf))
 			break;
-		}
 
 		/*
 		 * We got a valid link.  readlink() doesn't terminate strings