btrfs: fix function name in comment for btrfs_remove_ordered_extent()

Due to a refactoring introduced by commit 53d9981c ("btrfs: split
btrfs_alloc_ordered_extent to allocation and insertion helpers"), the
function btrfs_alloc_ordered_extent() was renamed to
alloc_ordered_extent(), so the comment at btrfs_remove_ordered_extent()
is no longer very accurate. Update the comment to refer to the new
name "alloc_ordered_extent()".
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ordered-data.c

@@ -626,7 +626,7 @@ void btrfs_remove_ordered_extent(struct btrfs_inode *btrfs_inode,
 	freespace_inode = btrfs_is_free_space_inode(btrfs_inode);
 
 	btrfs_lockdep_acquire(fs_info, btrfs_trans_pending_ordered);
-	/* This is paired with btrfs_alloc_ordered_extent. */
+	/* This is paired with alloc_ordered_extent(). */
 	spin_lock(&btrfs_inode->lock);
 	btrfs_mod_outstanding_extents(btrfs_inode, -1);
 	spin_unlock(&btrfs_inode->lock);