ublk_drv: use flexible-array member instead of zero-length array

Eliminate the following coccicheck warning:
./drivers/block/ublk_drv.c:127:16-19: WARNING use flexible-array member instead
Signed-off-by: NYushan Zhou <katrinzhou@tencent.com>
Link: https://lore.kernel.org/r/20221018100132.355393-1-zys.zljxml@gmail.comReviewed-by: NMing Lei <ming.lei@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/block/ublk_drv.c

@@ -124,7 +124,7 @@ struct ublk_queue {
 	bool force_abort;
 	unsigned short nr_io_ready;	/* how many ios setup */
 	struct ublk_device *dev;
-	struct ublk_io ios[0];
+	struct ublk_io ios[];
 };
 
 #define UBLK_DAEMON_MONITOR_PERIOD	(5 * HZ)