audio policy: fix preferred device for mmap I/Os

In findPreferredDevice(), when handling mmap I/Os, only clients for
the considered strategy/capture preset must be retained.

Bug: 345044066
Bug: 338143144
Flag: EXEMPT bug fix
Test: repro steps in the bug
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:8e70cf81e2c24e4f9e0b62b1cc78b0cf3ae4d0ef)
Merged-In: Ie4efbf3a6d2c2651c81a1aabd82e3f42a62f8d39
Change-Id: Ie4efbf3a6d2c2651c81a1aabd82e3f42a62f8d39