Fixed temporary brightness getting stuck bug.

When the user would set the brightness to the same value, the
temporary brightness would remain applied, effectively disabling
auto-brightness and confusing the system state.

Test: Drag the slider to an extremity (e.g. maximum), let it go, and
      then re-drag the slider to the same place (e.g. place your finger
      on the middle of the slider and move it to the maximum again).
      run adb shell dumpsys display | grep mAppliedTemporaryBrightness
      to check whether temporary brightness is applied; should be false.

Change-Id: Id3a1bff533b1bee9ca760e742dab379eeeb4b14e
Fixes: 111050860