adhd: Replace the use of master_linear_gain to main_linear_gain

Ableist language like master should be removed.
Replace the use of master_linear_gain to main_linear_gain.

BUG=b:167649426
TEST=Built and run cras successfully.

Change-Id: Ib90a0717fbbafb3cf99f9967b24e2c20beb2a2b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/adhd/+/2739022
Reviewed-by: En-Shuo Hsu <enshuo@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
Commit-Queue: Yu-Hsuan Hsu <yuhsuan@chromium.org>
Tested-by: Yu-Hsuan Hsu <yuhsuan@chromium.org>
4 files changed