Remove incorrect free() in zfs_get_pci_slots_sys_path()

Coverity found this. We attempted to free tmp, which is a pointer to a
string that should be freed by the caller.

Reviewed-by: Neal Gompa <ngompa@datto.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #13864

lib/libzutil/os/linux/zutil_device_path_os.c

@@ -273,7 +273,6 @@ zfs_get_pci_slots_sys_path(const char *dev_name)
 			free(address2);
 			if (asprintf(&path, "/sys/bus/pci/slots/%s",
 			    ep->d_name) == -1) {
-				free(tmp);
 				continue;
 			}
 			break;