ff_formats_ref() takes a pointer to an AVFilterFormats and a pointer to
a pointer to an AVFilterFormats as arguments and adds the latter as an
owner to the list pointed to by the former; the latter is hereby always
the address of a list contained in an AVFilterFormatsConfig and can
therefore not be NULL. So remove the check for whether it is NULL; also
do the same for ff_channel_layouts_ref().

Also do the same for the unref functions where argument is never NULL
because it is always the address of an existing lvalue.
Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>