aoc/alsa: return the heap address for mmap use cases

Some applications may stop the mmap stream but not close it.
Audio HAL will fail to get the dma-buf fd at the next stream,
then it will fall back to use the shared mode fd(/dev/snd).

Since AoC hooks the ring buffer address to the dma-buf heap
address, we return the same heap address in pcm mmap function
for mmap playback and capture use cases.

Bug:198963233
Test: 1. b/199285450#comment1, test_steal_exclusive -c0
      2. OboeTester

Signed-off-by: millerliang <millerliang@google.com>
Change-Id: I61d6e041507a385eb9f36d4a773f6751b542ada9