GBA Video: Fix map cache for 256-color mode 0 backgrounds
GBA Video: Fix map cache for 256-color mode 0 backgrounds

libretro/mgba,mgba-emu/mgba,libretro/mgba,Iniquitatis/mgba,mgba-emu/mgba,Iniquitatis/mgba,mgba-emu/mgba,libretro/mgba,libretro/mgba,Anty-Lemon/mgba,libretro/mgba,Anty-Lemon/mgba,Iniquitatis/mgba,Iniquitatis/mgba,mgba-emu/mgba,Anty-Lemon/mgba,Anty-Lemon/mgba