drm/gem: use _unlocked reference in drm_gem_objects_lookup docs

Use the drm_gem_object_put_unlocked in the documentation for
drm_gem_objects_lookup. The locked version of the helper should be used
solely by people who know exactly what they are doing.

Should prevent issues like ones adddressed with the next patch.
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20200515095118.2743122-3-emil.l.velikov@gmail.com

drivers/gpu/drm/drm_gem.c

@@ -690,7 +690,7 @@ static int objects_lookup(struct drm_file *filp, u32 *handle, int count,
  * Returns:
  *
  * @objs filled in with GEM object pointers. Returned GEM objects need to be
- * released with drm_gem_object_put(). -ENOENT is returned on a lookup
+ * released with drm_gem_object_put_unlocked(). -ENOENT is returned on a lookup
  * failure. 0 is returned on success.
  *
  */