GB Video: Fix writing to SGBC transparent BG colors (fixes #2367)
GB Video: Fix writing to SGBC transparent BG colors (fixes #2367)

Iniquitatis/mgba,mgba-emu/mgba,libretro/mgba,libretro/mgba,libretro/mgba,Iniquitatis/mgba,mgba-emu/mgba,mgba-emu/mgba,Iniquitatis/mgba,Iniquitatis/mgba,libretro/mgba,mgba-emu/mgba,libretro/mgba