null_blk: fix module name at log message

The name of the module is "null_blk", not "null". Make `pr_info()` follow
the pattern of `pr_err()` log messages.
Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/null_blk_main.c

@@ -1315,7 +1315,7 @@ static bool should_requeue_request(struct request *rq)
 
 static enum blk_eh_timer_return null_timeout_rq(struct request *rq, bool res)
 {
-	pr_info("null: rq %p timed out\n", rq);
+	pr_info("null_blk: rq %p timed out\n", rq);
 	blk_mq_complete_request(rq);
 	return BLK_EH_DONE;
 }
@@ -1812,7 +1812,7 @@ static int __init null_init(void)
 		}
 	}
 
-	pr_info("null: module loaded\n");
+	pr_info("null_blk: module loaded\n");
 	return 0;
 
 err_dev: