backend: fix runtime when used with thinktime

backend: fix runtime when used with thinktime

Runtime for fio jobs when used in conjuction with thinktime,
thinktime_iotime and thinktime_spin were sometimes more than
what is specified. Add a fix so that fio doesn't spin or sleep
for any duration beyond runtime.

For the first cycle fio starts by doing I/O for
thinktime + thinktime_iotime, which should just be for
thinktime_iotime. Add a fix for that.

Signed-off-by: Ankit Kumar <ankit.kumar@samsung.com>
Link: https://lore.kernel.org/r/20230217070322.14163-2-ankit.kumar@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>