Btrfs: only fua the first superblock when writting supers

We only intent to fua the first superblock in every device from
comments, fix it.

Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 0400a26..9850a51 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3133,7 +3133,10 @@
 		 * we fua the first super.  The others we allow
 		 * to go down lazy.
 		 */
-		ret = btrfsic_submit_bh(WRITE_FUA, bh);
+		if (i == 0)
+			ret = btrfsic_submit_bh(WRITE_FUA, bh);
+		else
+			ret = btrfsic_submit_bh(WRITE_SYNC, bh);
 		if (ret)
 			errors++;
 	}