GBA: Fix unintialized stack variable
GBA: Fix unintialized stack variable

cassos/mgba,cassos/mgba,Touched/mgba,sergiobenrocha2/mgba,Touched/mgba,Touched/mgba,jeremyherbert/mgba,iracigt/mgba,jeremyherbert/mgba,sergiobenrocha2/mgba,askotx/mgba,MerryMage/mgba,libretro/mgba,zerofalcon/mgba,sergiobenrocha2/mgba,bentley/mgba,fr500/mgba,Iniquitatis/mgba,sergiobenrocha2/mgba,Iniquitatis/mgba,iracigt/mgba,fr500/mgba,libretro/mgba,libretro/mgba,jeremyherbert/mgba,Iniquitatis/mgba,zerofalcon/mgba,iracigt/mgba,mgba-emu/mgba,AdmiralCurtiss/mgba,zerofalcon/mgba,bentley/mgba,iracigt/mgba,askotx/mgba,AdmiralCurtiss/mgba,MerryMage/mgba,Anty-Lemon/mgba,askotx/mgba,askotx/mgba,Iniquitatis/mgba,sergiobenrocha2/mgba,mgba-emu/mgba,Anty-Lemon/mgba,matthewbauer/mgba,jeremyherbert/mgba,fr500/mgba,libretro/mgba,cassos/mgba,matthewbauer/mgba,mgba-emu/mgba,Anty-Lemon/mgba,Anty-Lemon/mgba,mgba-emu/mgba,fr500/mgba,MerryMage/mgba,libretro/mgba,AdmiralCurtiss/mgba