Fix typo in blktrace code

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/blktrace.c b/blktrace.c
index 988ce59..c9141f6 100644
--- a/blktrace.c
+++ b/blktrace.c
@@ -70,7 +70,7 @@
 	if ((t->action & 0xffff) != __BLK_TA_QUEUE)
 		return;
 
-	w = (t->action & BLK_TC_ACT(BLK_TC_WRITE)) != 0;
+	rw = (t->action & BLK_TC_ACT(BLK_TC_WRITE)) != 0;
 	store_ipo(td, t->sector, t->bytes, rw);
 }