ASoC: msm8974: Fix external speaker power amp shutdown sequence

External speaker power amplifier should be disabled when all
the lineout power amplifiers are shutdown. When lineout is
shutdown bit mask was not cleared, due to which external power
amplifier will not be shutdown. Change clears the
bit mask for each lineout that is powered down.

Change-Id: I740653cbb6605708b38c915d59415f5b7f0c6d74
CRs-fixed: 497619
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>