ioat: Use time_before_jiffies()

To be future-proof and for better readability the time comparisons are modified
to use time_before_jiffies() instead of plain, error-prone math.

Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de>
[djbw: use time_before_jiffies() to make argument order more clear]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>