ath79: fix USB power GPIO for TP-Link TL-WR810N v1

ath79: fix USB power GPIO for TP-Link TL-WR810N v1

The TP-Link TL-WR810N v1 is known to cause soft-brick on ath79 and
work fine for ar71xx [1]. On closer inspection, the only apparent
difference is the GPIO used for the USB regulator, which deviates
between the two targets.

This applies the value from ar71xx to ath79.

Tested successfully by a forum user.

[1] https://forum.openwrt.org/t/tp-link-tl-wr810n-v1-ath79/48267

Fixes: cdbf2de77768 ("ath79: Add support for TP-Link WR810N")
Fixes: FS#3522
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>