ASoC: msm: Configure correct gain on set Volume command

Output channel gain is product of per channel gain and master gain.
Hence if only per channel gain is set and master gain is set to 0
then no audio is heard at the output.
Ensure that if we change per channel gain then we set master gain
to unity and vice versa. This enables only one gain to be effective.

Change-Id: I4cc2990efbb3e86edcc3d4328761cb64ed8fa775
Signed-off-by: Ashish Jain <ashishj@codeaurora.org>