wifi: iwlwifi: handle NULL/ERR returns from ptp_clock_register()

wifi: iwlwifi: handle NULL/ERR returns from ptp_clock_register()

ptp_clock_register() returns NULL when PTP support is disabled and may
return an ERR_PTR() on other failures. Reduce Log severity for NULL
return cases to avoid misleading errors when PTP is unavailable.

Signed-off-by: Avinash Bhatt <avinash.bhatt@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20260321192637.adea594600e8.I0e3d3f7ce897c54fff8ace6dd0faf55b4f39832b@changeid