wilc1000: copy address before calling wilc_set_mac_address

wilc_set_mac_address() calls IO routines which don't guarantee
the pointer won't be written to. Make a copy.

Acked-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>