volume: Fix reporting of pulse volume
volume: Fix reporting of pulse volume

While recalculating volume to percentage the result wasn't correctly
rounded. This caused the information held by plugin volume be out of
sync with actual device state.
Then adjusting the volume by plugin-volume behaved strange.

pmattern/lxqt-panel,stefonarch/lxqt-panel,stefonarch/lxqt-panel,stefonarch/lxqt-panel,lxde/lxqt-panel,pmattern/lxqt-panel,lxde/lxqt-panel