dpaa_eth: remove duplicate increment of the tx_errors counter

The tx_errors counter is incremented by the dpaa_xmit caller.

Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
Signed-off-by: Madalin Bucur <madalin.bucur@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>