cfq-iosched: fix bad return value cfq_should_preempt()

Commit a6151c3a5c inadvertently reversed
a preempt condition check, potentially causing a performance regression.
Make the meta check correct again.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/cfq-iosched.c

@@ -2051,7 +2051,7 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
 	 * it's a metadata request and the current queue is doing regular IO.
 	 */
 	if (rq_is_meta(rq) && !cfqq->meta_pending)
-		return false;
+		return true;
 
 	/*
 	 * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice.