CRAS: Only set dev format from the audio thread.

Since the format converter now lives in the audio thread, there is no
need to update the format of the rstream based on the device format.
Now set the device format when adding the first stream in the audio
thread.

BUG=none
TEST=unittest, plus play and record audio with multiple test clients.

Change-Id: I7288529e73a27b78a60c9076442577018e4aa47e
Signed-off-by: Dylan Reid <dgreid@chromium.org>
wip: src on server for input

Change-Id: Id7231f1eacdd649776f84020dae8659e8b4fef60
wip dev_stream tests capture

Change-Id: I011bafd46c7920be2d8301e70133f7f94645b992
wip: capture src 48 to 44.1 still has dropouts

Change-Id: Ife9784074ec8031e55939cf1caad67f8b1a9a7f4