[libretro] fixed core resolution changes detection
[libretro] fixed core resolution changes detection

frangarcj/Genesis-Plus-GX,frangarcj/Genesis-Plus-GX,Oggom/Genesis-Plus-GX,frangarcj/Genesis-Plus-GX,DavidKnight247/Genesis-Plus-GX,Oggom/Genesis-Plus-GX,DavidKnight247/Genesis-Plus-GX,DavidKnight247/Genesis-Plus-GX,frangarcj/Genesis-Plus-GX,Oggom/Genesis-Plus-GX,DavidKnight247/Genesis-Plus-GX,Oggom/Genesis-Plus-GX