btrfs: make end_extent_writepage return void

Does not return any errors, nor anything from the callgraph.  The branch
in end_bio_extent_writepage has been skipped since
5fd02043553b ("Btrfs: finish ordered extents in their own thread").

Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 2d57166..81f84f1 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -357,7 +357,7 @@
 		      int mirror_num);
 int clean_io_failure(struct inode *inode, u64 start, struct page *page,
 		     unsigned int pg_offset);
-int end_extent_writepage(struct page *page, int err, u64 start, u64 end);
+void end_extent_writepage(struct page *page, int err, u64 start, u64 end);
 int repair_eb_io_failure(struct btrfs_root *root, struct extent_buffer *eb,
 			 int mirror_num);