Fix the double PCM open during HFP call

If the second call is receving during a HFP call, audio path may change
to deep-buffer for ringtone playback intermediately and then come
back to HFP. So in this case, just keep the previsous opened PCM instead
of re-opening the PCM.

Bug: 66324788
Change-Id: I37666dac2602dc6d9d57a7fedc5a33f04890c1b5
(cherry picked from commit 74ab78e8356119b01f5d23d82221d8e2d5c9b3ac)