rt2x00: Fix quality/activity led handling

There was an obvious typo in LED structure
initialization which caused the radio and quality/activity
leds to be incorrectly initialized which resulted in
the leds not being enabled.

Additionally add the rt2x00led_led_activity() handler
that will enable TX/RX activity leds when the radio
is being enabled.

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