ath79: ubnt-amplifi-hd: Add 2nd USB bus (integrated ath3k bluetooth)

ath79: ubnt-amplifi-hd: Add 2nd USB bus (integrated ath3k bluetooth)

Add/enable 2nd USB bus (integrated ath3k bluetooth) to dts. This already
exists in the qca956x dtsi, adding the pointer here to bring the bluetooth to life.

The 2nd bus hosts the integrated bluetooth at 0x1b400000.

See in the comments for more info:
https://github.com/openwrt/openwrt/commit/c5b7ec8cee497c3a84eb8ad90d88494f0812698c

Tested-by: Russ Innes <russ.innes@gmail.com> on Ubiquiti Amplifi HD .
Signed-off-by: Russ Innes <russ.innes@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/19303
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>