Explicitly define on_output_devices_changed with void

For some reason this makes -fsanitize=function happy and gets rid of:
cras/src/tests/stream_apm_unittest.cc:438:3: runtime error: call to function (unknown) through pointer to incorrect function type 'void (*)()'
(/var/cache/portage/media-sound/adhd/06f28d5772d1404a84774cbe385179a7/execroot/adhd/bazel-out/amd64-dbg/bin/cras/src/tests/stream_apm_unittest+0xef248): note: (unknown) defined here
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior cras/src/tests/stream_apm_unittest.cc:438:3
Error: cras/src/tests/stream_apm_unittest: failed with exit code 1

BUG=b:445167544
TEST=FEATURES='-usersandbox test' emerge-amd64-generic adhd

Change-Id: I6d4746210063f26c940f39e05bb3570781bb1f3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/adhd/+/6968558
Tested-by: chromeos-cop-builder@chromeos-cop.iam.gserviceaccount.com <chromeos-cop-builder@chromeos-cop.iam.gserviceaccount.com>
Reviewed-by: Hsinyu Chao <hychao@chromium.org>
Commit-Queue: Li-Yu Yu <aaronyu@google.com>

Author: afq984

cras/src/server/cras_apm_reverse.h

@@ -44,7 +44,7 @@ typedef int (*process_reverse_needed_t)(bool default_reverse,
 /* Function to be triggered when the output devices has changed and
  * cause APM reverse modules state changes. Called in main thread.
  */
-typedef void (*output_devices_changed_t)();
+typedef void (*output_devices_changed_t)(void);
 
 /* Initializes APM reverse module with utility functions passed in. Called
  * in main thread.

cras/src/server/cras_stream_apm.c

@@ -1107,7 +1107,7 @@ static int send_apm_message(enum APM_THREAD_CMD cmd) {
 
 /* Triggered in main thread when devices state has changed in APM
  * reverse modules. */
-static void on_output_devices_changed() {
+static void on_output_devices_changed(void) {
   int rc;
   /* Send a message to audio thread because we need to access
    * |active_apms|. */