Btrfs: BUG to BUG_ON changes

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 3fdadd2..768b952 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -253,8 +253,7 @@
 
 	if (ret) {
 		printk(KERN_ERR "btrfs: unable to add free space :%d\n", ret);
-		if (ret == -EEXIST)
-			BUG();
+		BUG_ON(ret == -EEXIST);
 	}
 
 	return ret;