ath5k: sparse fix ath5k_led_on needs to be static

drivers/net/wireless/ath/ath5k/led.c:81:6: warning:
symbol 'ath5k_led_on' was not declared. Should it be static?

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>