block: Allow 0ms deadline latency and increase the read speed

Change a timer compare from after to after-equals, thus allowing 0 timeout
and making deadline and sio I/O schedulers FIFO.

Signed-off-by: xiaobing tu <xiaobing.tu@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: zwliew <zhaoweiliew@gmail.com>

Conflicts:
	block/zen-iosched.c

Change-Id: Ia9dad461c332eab78d435402bba9a075b6c2eda2