CRAS: dev_io - Don't appy software gain if APM is used

When CRAS APM is used for a stream, it wants full control to
the input gain, and doesn't want additional gain between CRAS
and browser APM.

BUG=chromium:891587
TEST=Manual test with tuned APM config, measure between
CRAS and browser's aecdump.

Change-Id: I0bc1dbc523d173a50746b6fe24b34eaaa5c757f2
Reviewed-on: https://chromium-review.googlesource.com/1267581


Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Hsinyu Chao <hychao@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>