CRAS: loopbacl_iodev - Fix get_buffer callback

Get buffer should not return frames more than requrested.

BUG=chromium:657510
TEST=cras_test_client --loopback_file /tmp/loopback

Change-Id: Ie789cbff30ede279e63e67f5822c36ab8a8c4dc7
Reviewed-on: https://chromium-review.googlesource.com/414750
Commit-Ready: Hsinyu Chao <hychao@chromium.org>
Tested-by: Hsinyu Chao <hychao@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
Reviewed-by: Chinyue Chen <chinyue@chromium.org>
1 file changed