ath9k: Fix LED GPIO pin for AR9462

GPIO pin 4 is assigned AR9462 chipsets LED.
while GPIO pin 0 worked for obselete AR9462 chipsets though
they are meant for EEPROM as per Russell

Cc: Senthil Balasubramanian <senthilb@qca.qualcomm.com>
Signed-off-by: Russell Hu <rhu@qca.qualcomm.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>