net: fs_enet: Fix wrong check in do_pd_setup

Should check of_iomap return value 'fep->fec.fecp' instead of 'fep->fcc.fccp'

Fixes: 976de6a8 ("fs_enet: Be an of_platform device when CONFIG_PPC_CPM_NEW_BINDING is set.")
Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>