md: the bitmap code needs to use blk_plug_device_unlocked()

It doesn't hold the queue lock, so it's both racey on the queue flags
and thus spews a warning.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 621a272..7e65bad 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -1234,7 +1234,7 @@
 		case 0:
 			bitmap_file_set_bit(bitmap, offset);
 			bitmap_count_page(bitmap,offset, 1);
-			blk_plug_device(bitmap->mddev->queue);
+			blk_plug_device_unlocked(bitmap->mddev->queue);
 			/* fall through */
 		case 1:
 			*bmc = 2;