Fix 32-bit compile warning in should_check_rate()

Introduced with the change from unsigned long -> uint64_T

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fio.h b/fio.h
index ed793ae..1ff384f 100644
--- a/fio.h
+++ b/fio.h
@@ -792,7 +792,7 @@
 }
 
 static inline int should_check_rate(struct thread_data *td,
-				    unsigned long *bytes_done)
+				    uint64_t *bytes_done)
 {
 	int ret = 0;