CRAS: audio_thread - allow input device to be specified to read_streams.
CRAS: audio_thread - allow input device to be specified to read_streams.

This will allow for the read_streams code to be re-used by loopback.

BUG=chromium:304346
TEST=record audio at different sample rates. audio_thread_unittest

Change-Id: I396cd36f113be76d1bbf3819d7322ff0acd2c9b1
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/172199

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