ASoC: msm: qdsp6v2: force sending stereo volume for mono

Certain AAC has channel switch, so DSP decoder might reconfigure output
from mono to stereo in runtime. If only volume of FC is sent, output
pcm won't get applied with volume setting properly. We should force
sending FL/FR/FC volume gain for mono clips.

Change-Id: I656080f32053f1dc866d8cd981a9d5f03c2d963a
CRs-Fixed: 924685
Signed-off-by: Weiyin Jiang <wjiang@codeaurora.org>