getInputForAttr perm check cleanup pt2

Update param types for AudioPolicyManager::getInputForAttr to avoid
ptrs/inout for clarity.

No behavior changes for now.

Test: CtsMediaAudioTestCases
Bug: 374870131
Bug: 343523722
Flag: EXEMPT mechanical refactoring

Change-Id: Ic179b09159b47b5af5a56811af9ef759e47eea0c