ath79: fix LEDs for GL.inet GL-AR150

ath79: fix LEDs for GL.inet GL-AR150

Since the wireless LED was used for boot and set up with a DT
trigger, the WiFi indication hasn't worked on ath79 at all.

In addition, a look into the manual revealed that the OEM
configuration is as follows:

LED 1 (green): power
LED 2 (green): configurable
LED 3 (red): wireless

So, let's just keep the WiFi trigger and convert the rest to its
"intended" use.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
(cherry picked from commit 705fe43522c756962589b360141d4c398363ce1c)