net: dsa: mv88e6xxx: rename port cmode macro

This is a cosmetic update. We are removing the last underscore from
macros MV88E6XXX_PORT_STS_CMODE_100BASE_X and
MV88E6XXX_PORT_STS_CMODE_1000BASE_X. The 2500base-x version does not
have that underscore. Also PHY_INTERFACE_MODE_ macros do not have it
there.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>