cfq-iosched: fix bad return value cfq_should_preempt()

Commit a6151c3a5c8e1ff5a28450bc8d6a99a2a0add0a7 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>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 069a610..5802e32 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2051,7 +2051,7 @@
 	 * 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.