btrfs: use test_and_clear_bit() in wait_dev_flush()

The function wait_dev_flush() tests for the BTRFS_DEV_STATE_FLUSH_SENT
bit and then clears it separately. Instead, use test_and_clear_bit().
Though we don't need to do the atomic test and clear, it's following a
common pattern.
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -4122,10 +4122,9 @@ static bool wait_dev_flush(struct btrfs_device *device)
 {
 	struct bio *bio = &device->flush_bio;
 
-	if (!test_bit(BTRFS_DEV_STATE_FLUSH_SENT, &device->dev_state))
+	if (!test_and_clear_bit(BTRFS_DEV_STATE_FLUSH_SENT, &device->dev_state))
 		return false;
 
-	clear_bit(BTRFS_DEV_STATE_FLUSH_SENT, &device->dev_state);
 	wait_for_completion_io(&device->flush_wait);
 
 	if (bio->bi_status) {