btrfs: use enum for wq endio metadata type

The enum exists but is not consistently used.

Signed-off-by: David Sterba <dsterba@suse.cz>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 344a322..b1e388d 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7721,7 +7721,8 @@
 	bio_get(bio);
 
 	if (!write) {
-		ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
+		ret = btrfs_bio_wq_end_io(root->fs_info, bio,
+				BTRFS_WQ_ENDIO_DATA);
 		if (ret)
 			goto err;
 	}