audio: Prolong reading attempts from the remote submix pipe

In order to use the time interval for reading from the remote
submix pipe more efficiently, increase the deadline time
to the buffer duration minus a small amount. This should
minimize chances to have discontinuities in the remote submix
input.

Bug: 334363414
Test: atest --test-filter=".*RemoteSubmixTest#testRemoteSubmixRecordingContinuity" CtsMediaAudioTestCases
Change-Id: I02968d09afd8ecdad4d61e635393842d7280e55f