libaudiohal: Modify calculation of buffer duration for mmap streams am: 0f5e339e

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/27552789



Change-Id: If4196ae492a0f18305de882fd0dc7e871e5550c3
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>