dpaa2-eth: fix uninitialized variable warnings

All 3 cases of possible uninitialized variables are false
positives since they are used only as output parameters.
Nonetheless, fix the warnings.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>