Sony Xperia 5 III headphone gain boost for magisk

Only for Sony Xperia 5 III running LineageOS 21.0

Changes values in /vendor/etc/audio/sku_lahaina/mixer_paths.xml for RX_Digital_Volume in order to set the "master" volume for headphone out (3.5mm jack) to "84". After that, every individual volume step will scale accordingly. This value has been well tested to not cause any distortions at max. volume.