rt2x00: Fix LED configuration setting for rt2800.

rt2800_blink_set uses an illegal value to set the LED_CFG_G_LED_MODE
field of the LED_CFG register. This field is only 2 bits large, so
should be initialized with value that fits. Use default value from
the vendor driver.

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>