btrfs: update stale comment for log_new_dir_dentries()

The comment refers to the function log_dir_items() in order to check why
the inodes of new directory entries need to be logged, but the relevant
comments are no longer at log_dir_items(), they were moved to the function
process_dir_items_leaf() in commit eb10d85ee7 ("btrfs: factor out the
copying loop of dir items from log_dir_items()"). So update it with the
current function name.

Also remove references with i_mutex to "VFS lock", since the inode lock
is no longer a mutex since 2016 (it's now a rw semaphore).

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-log.c

@@ -6073,12 +6073,12 @@ struct btrfs_dir_list {
 };
 
 /*
- * Log the inodes of the new dentries of a directory. See log_dir_items() for
- * details about the why it is needed.
+ * Log the inodes of the new dentries of a directory.
+ * See process_dir_items_leaf() for details about why it is needed.
  * This is a recursive operation - if an existing dentry corresponds to a
  * directory, that directory's new entries are logged too (same behaviour as
  * ext3/4, xfs, f2fs, reiserfs, nilfs2). Note that when logging the inodes
- * the dentries point to we do not lock their i_mutex, otherwise lockdep
+ * the dentries point to we do not acquire their VFS lock, otherwise lockdep
  * complains about the following circular lock dependency / possible deadlock:
  *
  *        CPU0                                        CPU1
@@ -6090,7 +6090,7 @@ struct btrfs_dir_list {
  *
  * Where sb_internal is the lock (a counter that works as a lock) acquired by
  * sb_start_intwrite() in btrfs_start_transaction().
- * Not locking i_mutex of the inodes is still safe because:
+ * Not acquiring the VFS lock of the inodes is still safe because:
  *
  * 1) For regular files we log with a mode of LOG_INODE_EXISTS. It's possible
  *    that while logging the inode new references (names) are added or removed