gma500: unload fixes

Debugging the lid problem tested various error paths which were found
wanting so start fixing them up.

There is a ton of improvement work could be done here so that every bit
of functionality agrees if its _fini, _uninit, etc, and they agree who
is responsible for deciding if the clean up is needed.

That can come later.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>