net: phy: mscc: use new PTP_MSGTYPE_* defines

Use recently introduced PTP_MSGTYPE_SYNC and PTP_MSGTYPE_DELAY_REQ
defines instead of a driver internal enumeration.

Signed-off-by: Christian Eggers <ceggers@arri.de>
Reviewed-by: Antoine Tenart <atenart@kernel.org>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>