Amethyst internal PHYs also report empty model number in MII_PHYSID2.

Fill in switch product number, as is done for Topaz and Peridot.
Signed-off-by: NMarek Behún <kabel@kernel.org>
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>