Volume can not be updated in Sound&notification

After "onActivityPause()" is invoked and "onActivityResume()"
is invoked again, "mVolumizer" is not empty object,
so volume is not updated.

To fix this issue, set "mVolumizer" is null in "onActivityPause()",
if "onActivityResume()" is invoked again, recreate "mVolumizer"
and update volume.

Bug: 37558283

Change-Id: Id91064ea32305b5bf203f34e31988ac923beee6d