net: fman: Specify type of mac_dev for exception_cb

Instead of using a void pointer for mac_dev, specify its type
explicitly.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Acked-by: Camelia Groza <camelia.groza@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>