net: netcp: drop kfree for memory allocated with devm_kzalloc

It's not necessary to free memory allocated with devm_kzalloc in the
remove path and using kfree leads to a double free.

Fixes: 84640e27 ("net: netcp: Add Keystone NetCP core ethernet
driver")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>