cras: floop: double the buffer size

Chrome input stream runs on callback threshold 4800 due to
processing function. Double the buffer size to make sure that the
callback threshold is less than half of buffer size.

BUG=b:327533160
TEST=use arcvm to playback audio with live caption /
     cras_test_client --follow_at | grep OVERRUN shows nothing

Change-Id: Iaa57502b3d1d3e3667a39923e0017b95f8975289
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/adhd/+/5568412
Commit-Queue: Terry Cheong <htcheong@chromium.org>
Reviewed-by: Yu-Hsuan Hsu <yuhsuan@chromium.org>
Reviewed-by: Li-Yu Yu <aaronyu@google.com>
Tested-by: chromeos-cop-builder@chromeos-cop.iam.gserviceaccount.com <chromeos-cop-builder@chromeos-cop.iam.gserviceaccount.com>

cras/src/server/cras_floop_iodev.c

@@ -54,7 +54,7 @@
  * to check for floop odevs that the stream should be attached to.
  */
 
-#define LOOPBACK_BUFFER_SIZE 8192
+#define LOOPBACK_BUFFER_SIZE 16384
 
 static size_t loopback_supported_rates[] = {48000, 0};