From: Christoph Hellwig <hch@lst.de>

Take a reference before calling into the module and release it after we're
done.  Also remove the useless (and wrong) refcounting in videocodec -
symbols from this module are used by other modules if we call into those
functions so it can't be unloaded anyway.

We really need to add a debug check to tip all those
try_module_get(THIS_MODULE) callers..