net: mvpp2: 10G modes aren't supported on all ports

The mvpp2_phylink_validate() function sets all modes that are
supported by a given PPv2 port. A recent change made all ports to
advertise they support 10G modes in certain cases. This is not true,
as only the port #0 can do so. This patch fixes it.

Fixes: 01b3fd5a ("net: mvpp2: fix detection of 10G SFP modules")
Cc: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>