Change a few functions that only ever returned 0 to voids

Change a few functions that only ever returned 0 to voids

These are internal functions, if we need them to return an error code we can
change that at any time. Meanwhile, if we only ever return 0 anyway we might
as well just make them voids to save on error paths.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Yong Bakos <ybakos@humanoriented.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>