alsa_sound: Clean-up of previous Resampler for A2DP device

-During Playback, While switching from AOA USB Device to BT
 Headset, silence heard on BT headset with intermittent
 down-sampled sound.
-For AOA USB, a Resampler is using and its not getting free
 when switching to BT headset, thus Resampler is also using
 for A2DP device that is leading to down-sampled sound and
 silence.
-Releasing resampler during switchExtOut for A2DP case.

Change-Id: I8879be11886ebe482a87f8b7191582a755d7c3d7
CRs-Fixed: 568306