btrfs: btrfs_drop_snapshot should return int

Commit cb1b69f4 (Btrfs: forced readonly when btrfs_drop_snapshot() fails)
made btrfs_drop_snapshot return void because there were no callers checking
the return value. That is the wrong order to handle error propogation since
the caller will have no idea that an error has occured and continue on
as if nothing went wrong.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 6e256d9..fb5cd5a 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1387,6 +1387,8 @@
 	spin_unlock(&fs_info->trans_lock);
 
 	while (!list_empty(&list)) {
+		int ret;
+
 		root = list_entry(list.next, struct btrfs_root, root_list);
 		list_del(&root->root_list);
 
@@ -1394,9 +1396,10 @@
 
 		if (btrfs_header_backref_rev(root->node) <
 		    BTRFS_MIXED_BACKREF_REV)
-			btrfs_drop_snapshot(root, NULL, 0, 0);
+			ret = btrfs_drop_snapshot(root, NULL, 0, 0);
 		else
-			btrfs_drop_snapshot(root, NULL, 1, 0);
+			ret =btrfs_drop_snapshot(root, NULL, 1, 0);
+		BUG_ON(ret < 0);
 	}
 	return 0;
 }