e1000: fix time comparison

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

Signed-off-by: Asaf Vertz <asaf.vertz@tandemg.com>
Acked-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>