ptp: bnxt: convert .adjfreq to .adjfine

When the BNXT_FW_CAP_PTP_RTC flag is not set, the bnxt driver implements
.adjfreq on a cyclecounter in terms of the straightforward "base * ppb / 1
billion" calculation. When BNXT_FW_CAP_PTP_RTC is set, the driver forwards
the ppb value to firmware for configuration.

Convert the driver to the newer .adjfine interface, updating the
cyclecounter calculation to use adjust_by_scaled_ppm to perform the
calculation. Use scaled_ppm_to_ppb when forwarding the correction to
firmware.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Cc: Michael Chan <michael.chan@broadcom.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>