GBA Audio: Increase PSG volume (fixes #749)

CHANGES

@@ -32,6 +32,7 @@ Bugfixes:
  - GBA Cheats: Fix slide codes not initializing properly
  - Qt: Fix locale being set to English on settings save (fixes mgba.io/i/906)
  - LR35902: Fix watchpoints not reporting new value
+ - GBA Audio: Increase PSG volume (fixes mgba.io/i/749)
 Misc:
  - GBA Timer: Use global cycles for timers
  - GBA: Extend oddly-sized ROMs to full address space (fixes mgba.io/i/722)

src/gba/audio.c

@@ -260,7 +260,7 @@ static void _sample(struct mTiming* timing, void* user, uint32_t cyclesLate) {
 	struct GBAAudio* audio = user;
 	int16_t sampleLeft = 0;
 	int16_t sampleRight = 0;
-	int psgShift = 5 - audio->volume;
+	int psgShift = 4 - audio->volume;
 	GBAudioSamplePSG(&audio->psg, &sampleLeft, &sampleRight);
 	sampleLeft >>= psgShift;
 	sampleRight >>= psgShift;