pch_phub: Fix MAC address writing issue for LAPIS ML7831

ISSUE:
Using ML7831, MAC address writing doesn't work well.

CAUSE:
ML7831 and EG20T have the same register map for MAC address access.
However, this driver processes the writing the same as ML7223.
This is not true.
This driver must process the writing the same as EG20T.
This patch fixes the issue.

Signed-off-by: Tomoya MORINAGA <tomoya.rohm@gmail.com>
Cc: Masayuki Ohtak <masa-korg@dsn.okisemi.com>
Cc: Alexander Stein <alexander.stein@systec-electronic.com>
Cc: Denis Turischev <denis@compulab.co.il>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>