av: Fix volume count sent to HAL

Use audio_channel_count_from_out_mask to properly calculate the
channel count from the mask, so a valid volume array can be
sent to audio hal.

Test: play a clip check volume array sent to hal
Bug: 326853618
(cherry picked from https://android-review.googlesource.com/q/commit:f4fc9eefcbf2b7fc9758686f12e3417edafbe368)
Merged-In: I59b815f8f4eb16b4aeb2941330b023320adf95e2
Change-Id: I59b815f8f4eb16b4aeb2941330b023320adf95e2