Audio: Add volume for alternate speed.

Fixes #11605.

Core/Config.cpp

@@ -779,6 +779,7 @@ static ConfigSetting soundSettings[] = {
 	ConfigSetting("ExtraAudioBuffering", &g_Config.bExtraAudioBuffering, false, true, false),
 	ConfigSetting("AudioResampler", &g_Config.bAudioResampler, true, true, true),
 	ConfigSetting("GlobalVolume", &g_Config.iGlobalVolume, VOLUME_MAX, true, true),
+	ConfigSetting("AltSpeedVolume", &g_Config.iAltSpeedVolume, -1, true, true),
 
 	ConfigSetting(false),
 };