audio: avoid muting already muted stream

-Issue: FM or music is getting mixed with ringtone over the
 speaker when BT or wired HS is connected. Because the stream will
 not get temporarily muted if its already muted.But during unmute,
 there is no condition to check whether stream is temporarily muted
 or not.This is leading to unmuting of non-muted stream
-Fix is added to avoid muting of stream if its already
 muted

CRs-Fixed: 574271
Change-Id: I6b4962f402b87781846e37aed1872a639d06f488