drbd: Fix drbd_request_prepare() discard handling

Fix the test that verifies whether bio_op(bio) represents a discard
or write zeroes operation. Compile-tested only.

Cc: Philipp Reisner <philipp.reisner@linbit.com>
Cc: Lars Ellenberg <lars.ellenberg@linbit.com>
Fixes: 7435e901 ("drbd: zero-out partial unaligned discards on local backend")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/drbd/drbd_req.c

@@ -1244,8 +1244,8 @@ drbd_request_prepare(struct drbd_device *device, struct bio *bio, unsigned long
 	_drbd_start_io_acct(device, req);
 
 	/* process discards always from our submitter thread */
-	if ((bio_op(bio) & REQ_OP_WRITE_ZEROES) ||
-	    (bio_op(bio) & REQ_OP_DISCARD))
+	if (bio_op(bio) == REQ_OP_WRITE_ZEROES ||
+	    bio_op(bio) == REQ_OP_DISCARD)
 		goto queue_for_submitter_thread;
 
 	if (rw == WRITE && req->private_bio && req->i.size