e1000e: convert .adjfreq to .adjfine

The PTP implementation for the e1000e driver uses the older .adjfreq
method. This method takes an adjustment in parts per billion. The newer
.adjfine implementation uses scaled_ppm. The use of scaled_ppm allows for
finer grained adjustments and is preferred over using the older
implementation.

Make use of mul_u64_u64_div_u64 in order to handle possible overflow of the
multiplication used to calculate the desired adjustment to the hardware
increment value.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Naama Meir <naamax.meir@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>