Btrfs: Fix some build problems on 2.6.18 based enterprise kernels

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 27a0237..d617c29 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -20,7 +20,7 @@
 #include <linux/pagemap.h>
 #include <linux/spinlock.h>
 #include <linux/page-flags.h>
-#include <linux/bug.h>
+#include <asm/bug.h>
 #include "ctree.h"
 #include "extent_io.h"
 #include "locking.h"