hal: Fix no Tx issue during multi party HFP calls

- When an incoming MT HFP call is accepted during an ongoing
  MO HFP call, the MO call goes to held state. Later, if this held
  call is rejected, Tx is not heard at the far end of the incoming
  call from that moment.
- When the held call is rejected, the input device gets disabled due
  to which Tx samples are not captured.
- Fix the issue by ensuring that the input device is not set to none when
  HFP is active.

CRs-Fixed: 656928
Change-Id: Ie3f0886c0412bfdb3e450c54e9f4b651e992f84e