sound/backlight: Invert scroll direction

Fixes #3.

src/backlight.rs

@@ -140,7 +140,7 @@ impl ModuleImpl for Backlight {
                 x: _x,
                 y,
             } => {
-                self.add(y as f32 / 800.0).unwrap();
+                self.add(y as f32 / -800.0).unwrap();
                 match self.sync() {
                     Ok(val) => val,
                     Err(err) => {

src/sound.rs

@@ -478,7 +478,7 @@ impl ModuleImpl for PulseAudio {
                 self.device
                     .lock()
                     .unwrap()
-                    .set_volume(y as f32 / 800.0)
+                    .set_volume(y as f32 / -800.0)
                     .unwrap();
             }
             Input::Click { pos: _pos, button } => match button {