net: hns3: fix variable may not initialized problem in hns3_init_mac_addr()

When a VF is calling hns3_init_mac_addr(), get_mac_addr() may
return fail, then the value of mac_addr_temp is not initialized.

Fixes: 76ad4f0e ("net: hns3: Add support of HNS3 Ethernet Driver for hip08 SoC")
Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Signed-off-by: Jijie Shao <shaojijie@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>