libaudiohal: Modify calculation of buffer duration for mmap streams

To calculate to buffer duration of mmap streams, use burst size.
Burst size gives proper timings about consumption of mmap buffers,
eventually adjusting the mLastReplyLifeTimeNs, which impacts query of
position from HAL.

Bug: 342529498
Test: run mmap usecase and check timestamp query interval.

Change-Id: Ibb88765da62e019bbb677fe0b1980bbf64e82073