Similar to c298ede2 ("net: bcmgenet: simplify circular pointer
arithmetic") we don't need to complex arthimetic since we always have a
ring size that is a power of 2.
Signed-off-by: NFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>