octeon_ep: ensure get mac address successfully before eth_hw_addr_set()

octep_get_mac_addr() can fail because send mbox message failed. If this
happens, octep_dev->mac_addr will be zero. It should not continue to
initialize. Add exception handling for octep_get_mac_addr() to fix it.

Fixes: 862cd659

 ("octeon_ep: Add driver framework and device initialization")
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>