e1000e: remove call to do_div and sign mismatch warning

e1000e: remove call to do_div and sign mismatch warning

Orabug: 21792108

Fixes a warning that was reported by Yanjiang Jin
<yanjiang.jin@windriver.com> by implementing the solution suggested by
Alexander Duyck <alexander.h.duyck@redhat.com>.

Signed-off-by: Yanir Lubetkin <yanirx.lubetkin@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit bfc9473bf90457bf31d3f675d82234897c6480cd)
Signed-off-by: Brian Maly <brian.maly@oracle.com>