btrfs: let writepage_end_io_hook return void

There's no error path in any of the instances, always return 0.
Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -2437,12 +2437,9 @@ void end_extent_writepage(struct page *page, int err, u64 start, u64 end)
 
 	tree = &BTRFS_I(page->mapping->host)->io_tree;
 
-	if (tree->ops && tree->ops->writepage_end_io_hook) {
-		ret = tree->ops->writepage_end_io_hook(page, start,
-					       end, NULL, uptodate);
-		if (ret)
-			uptodate = 0;
-	}
+	if (tree->ops && tree->ops->writepage_end_io_hook)
+		tree->ops->writepage_end_io_hook(page, start, end, NULL,
+				uptodate);
 
 	if (!uptodate) {
 		ClearPageUptodate(page);

fs/btrfs/extent_io.h

@@ -104,7 +104,7 @@ struct extent_io_ops {
 	int (*readpage_end_io_hook)(struct btrfs_io_bio *io_bio, u64 phy_offset,
 				    struct page *page, u64 start, u64 end,
 				    int mirror);
-	int (*writepage_end_io_hook)(struct page *page, u64 start, u64 end,
+	void (*writepage_end_io_hook)(struct page *page, u64 start, u64 end,
 				      struct extent_state *state, int uptodate);
 	void (*set_bit_hook)(struct inode *inode, struct extent_state *state,
 			     unsigned *bits);

fs/btrfs/inode.c

@@ -2972,7 +2972,7 @@ static void finish_ordered_fn(struct btrfs_work *work)
 	btrfs_finish_ordered_io(ordered_extent);
 }
 
-static int btrfs_writepage_end_io_hook(struct page *page, u64 start, u64 end,
+static void btrfs_writepage_end_io_hook(struct page *page, u64 start, u64 end,
 				struct extent_state *state, int uptodate)
 {
 	struct inode *inode = page->mapping->host;
@@ -2986,7 +2986,7 @@ static int btrfs_writepage_end_io_hook(struct page *page, u64 start, u64 end,
 	ClearPagePrivate2(page);
 	if (!btrfs_dec_test_ordered_pending(inode, &ordered_extent, start,
 					    end - start + 1, uptodate))
-		return 0;
+		return;
 
 	if (btrfs_is_free_space_inode(BTRFS_I(inode))) {
 		wq = fs_info->endio_freespace_worker;
@@ -2999,8 +2999,6 @@ static int btrfs_writepage_end_io_hook(struct page *page, u64 start, u64 end,
 	btrfs_init_work(&ordered_extent->work, func, finish_ordered_fn, NULL,
 			NULL);
 	btrfs_queue_work(wq, &ordered_extent->work);
-
-	return 0;
 }
 
 static int __readpage_endio_check(struct inode *inode,