block, bfq: don't dereference bic before null checking it

The call to bfq_check_ioprio_change will dereference bic, however,
the null check for bic is after this call.  Move the the null
check on bic to before the call to avoid any potential null
pointer dereference issues.

Detected by CoverityScan, CID#1430138 ("Dereference before null check")
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

block/bfq-iosched.c

@@ -4401,11 +4401,11 @@ static int bfq_get_rq_private(struct request_queue *q, struct request *rq,
 
 	spin_lock_irq(&bfqd->lock);
 
-	bfq_check_ioprio_change(bic, bio);
-
 	if (!bic)
 		goto queue_fail;
 
+	bfq_check_ioprio_change(bic, bio);
+
 	bfq_bic_update_cgroup(bic, bio);
 
 	bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, false, is_sync,