AAudio: Use one SRC per shared stream.

In ag/23541584, SRC was added to AAudio.
This caused issues with timestamps in shared streams.

We should use the default sample rate for the shared MMAP endpoint.
This way, each shared stream can use its own SRC.

Bug: 378766408
Test: atest AAudioTests
Test: OboeTester Test Output with shared stream and SRC
Flag: EXEMPT bugfix
Change-Id: I15c31630e770fb9ba75bfb30d41af568d386041f