net: spider_net: do not read mac address again after setting it

This patch removes the spider_net_get_mac_address() call at the end of
the spider_net_set_mac() function. The dev->dev_addr is instead updated
with a memcpy() from sa->sa_data.

Since spider_net_get_mac_address() is not used anywhere else, this patch
also removes the function.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>