hal: sampling rate mismatch during a2dp+spk combo usecase.

During a2dp+spk combo usecase, a2dp device is assigned with
sampling rate of speaker though requested sampling rate of
a2dp was different.

Fix this by moving assignment of speaker sampling rate after
the condition of a2dp+spk combo was validated.

Change-Id: Iae02657bea51807191d864964865465e558b919d