ath79: ar9330: fix switch_led_disable_pins reg value

ath79: ar9330: fix switch_led_disable_pins reg value

In commit e9652e1696d9 ("ath79: fix pinmux for ar933x devices") I've
wrongly changed desired register value to 0xf8 although it should've
been set to 0x0.

0xf8 value sets bits 3-7 (ETH_SWITCH_LEDx_EN) to 1 which actually
enables ethernet switch LEDs, so 0x0 is correct value in order to use
the pins as GPIO.

Fixes: e9652e1696d9 ("ath79: fix pinmux for ar933x devices")
Reported-by: Chuanhong Guo <gch981213@gmail.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>