audioflinger: fix recursive mutex locking

Commit 3e1acc0c introduced a possible recursive mutex locking when
an AudioRecord creation request with FAST flag is rejected by
AudioFlinger after the input was opened by audio policy.

Bug: 70388312
Test: AudioRecord CTS, Audio smoke tests
Change-Id: Ifc835fddd7e819600a834a8d058a9c98bddbee4e