ice: make ice_get_pf_c827_idx static

The ice_get_pf_c827_idx function is only called inside of ice_ptp_hw.c, so
there is no reason to export it. Mark it static and remove the declaration
from ice_ptp_hw.h

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: David S. Miller <davem@davemloft.net>