CacheFiles: name i_mutex lock class explicitly

Just some cleanup.

(And note the caller of this function may, for example, call vfs_unlink
on a child, so the "1" (I_MUTEX_PARENT) really was what was intended
here.)
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Tested-By: NMilosz Tanski <milosz@adfin.com>
Acked-by: NJeff Layton <jlayton@redhat.com>

fs/cachefiles/namei.c

@@ -836,7 +836,7 @@ static struct dentry *cachefiles_check_active(struct cachefiles_cache *cache,
 	//       dir->d_name.len, dir->d_name.len, dir->d_name.name, filename);
 
 	/* look up the victim */
-	mutex_lock_nested(&dir->d_inode->i_mutex, 1);
+	mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_PARENT);
 
 	start = jiffies;
 	victim = lookup_one_len(filename, dir, strlen(filename));