dpaa2-eth: mark unused parameter in dpaa2_eth_tx_conf

The ch parameter is never used in the dpaa2_eth_tx_conf function but
since its prototype must match the type defined in the consume field of
struct dpaa2_eth_fq, just mark it as __always_unused.

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