Btrfs: fix compiler warnings on 32 bit systems

The enospc tracing code added some interesting uses of
u64 pointer casts.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index b669a7d..d986824 100644
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -644,7 +644,7 @@
 static int btrfsic_process_superblock(struct btrfsic_state *state,
 				      struct btrfs_fs_devices *fs_devices)
 {
-	int ret;
+	int ret = 0;
 	struct btrfs_super_block *selected_super;
 	struct list_head *dev_head = &fs_devices->devices;
 	struct btrfs_device *device;