net: mvpp2: fix alignment of MVPP2_GMAC_CONFIG_MII_SPEED definition

Cosmetic patch fix the alignment of the MVPP2_GMAC_CONFIG_MII_SPEED
macro definition.
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>