net: aquantia: add an error handling in aq_nic_set_multicast_list
add an error handling in aq_nic_set_multicast_list, it may not
work when hw_multicast_list_set error; and at the same time
it will remove gcc Wunused-but-set-variable warning.
Signed-off-by: Chenwandun <chenwandun@huawei.com> Reviewed-by: Igor Russkikh <igor.russkikh@aquantia.com> Reviewed-by: Andrew Lunn <andrew@lunn.ch> Signed-off-by: David S. Miller <davem@davemloft.net>