block: bfq-iosched: fix duplicated word

Change "at at" to "at a".
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bfq-iosched.c

@@ -4714,7 +4714,7 @@ static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
 	 * some unlucky request wait for as long as the device
 	 * wishes.
 	 *
-	 * Of course, serving one request at at time may cause loss of
+	 * Of course, serving one request at a time may cause loss of
 	 * throughput.
 	 */
 	if (bfqd->strict_guarantees && bfqd->rq_in_driver > 0)