net: mvpp2: align values in ethtool get_coalesce

Cosmetic patch aligning values in the ethtool get_coalesce function.
This patch do not modify in anyway the driver's behaviour.
Signed-off-by: NAntoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>