net: stmmac: Fix misuses of GENMASK macro

Arguments are supposed to be ordered high then low.

Fixes: 293e4365 ("stmmac: change descriptor layout")
Fixes: 9f93ac8d

 ("net-next: stmmac: Add dwmac-sun8i")
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>