e1000e: remove unnecessary range check in e1000e_phc_adjfreq

The e1000e_phc_adjfreq function validates that the input delta is within
the maximum range. This is already handled by the core PTP code and this is
a duplicate and thus unnecessary check. It also complicates refactoring to
use the newer .adjfine implementation, where the input is no longer
specified in parts per billion. Remove the range validation check.

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>