drm: Remove opencoded drm_gem_object_release_handle()

drm_gem_handle_delete() contains its own version of
drm_gem_object_release_handle(), so lets just call the release method
instead.

Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1451986951-3703-2-git-send-email-chris@chris-wilson.co.uk


Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>