brcm80211: make ethtool_ops const

All usage of ethtool_ops should be const; also add comma at end
of initializer list.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>