refac: rename func_8030D90C to sfxsource_createSfxsourceAndReturnIndex and func_8030DBB4 to sfxsource_playSfxAtVolume

Additionally rename properties/variables assigned by sfxsource_createSfxsourceAndReturnIndex to sfxsourceIdx

src/GV/ch/histup.c

@@ -222,7 +222,7 @@ void func_8038DBDC(Actor *this){
                     if(1.0 < this->unk1C[1]){
                         this->unk1C[1] -= 0.1;
                     }
-                    func_8030DBB4(this->unk44_31, this->unk1C[1]);
+                    sfxsource_playSfxAtVolume(this->unk44_31, this->unk1C[1]);
                 }
             }
             break;