e1000e: e1000e_cyclecounter_read(): fix er32(SYSTIML) overflow check

If two consecutive reads of the counter are the same, it is also
not an overflow.  "systimel_1 < systimel_2" should be
"systimel_1 <= systimel_2".

Before the patch, we could perform an *erroneous* correction:

Let's say that systimel_1 == systimel_2 == 0xffffffff.
"systimel_1 < systimel_2" is false, we think it's an overflow,
we read "systimeh = er32(SYSTIMH)" which meanwhile had incremented,
and use "(systimeh << 32) + systimel_2" value which is 2^32 too large.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
CC: intel-wired-lan@lists.osuosl.org
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>