usb audio: Fix incorrect bytes returned for recording

 In a recording session , the number of bytes read is
 not updated when pcm_read() fails. This results in
 silence data being added during a device switch from
 USB headset to handset.
 Fix is to reset the number of bytes read if pcm_read()
 returns an error indicating removal of USB headset.

 CRs-Fixed: 753186

Change-Id: I10d578c3cf1037c90a891e63be2bd1c2b7e6126b