drm: Balance error path for GEM handle allocation

The current error path for failure when establishing a handle for a GEM
object is unbalance, e.g. we call object_close() without calling first
object_open(). Use the typical onion structure to only undo what has
been set up prior to the error.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>