block: Convert fifo_time from ulong to u64

Currently rq->fifo_time is unsigned long but CFQ stores nanosecond
timestamp in it which would overflow on 32-bit archs. Convert it to u64
to avoid the overflow. Since the rq->fifo_time is unioned with struct
call_single_data(), this does not change the size of struct request in
any way.

We have to slightly fixup block/deadline-iosched.c so that comparison
happens in the right types.

Fixes: 9a7f38c42c
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

include/linux/blkdev.h

@@ -90,7 +90,7 @@ struct request {
 	struct list_head queuelist;
 	union {
 		struct call_single_data csd;
-		unsigned long fifo_time;
+		u64 fifo_time;
 	};
 
 	struct request_queue *q;