wifi: mwl8k: initialize cmd->addr[] properly

This loop is supposed to copy the mac address to cmd->addr but the
i++ increment is missing so it copies everything to cmd->addr[0] and
only the last address is recorded.

Fixes: 22bedad3 ("net: convert multicast list to list_head")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/b788be9a-15f5-4cca-a3fe-79df4c8ce7b2@moroto.mountain