drm/gma500: Use lockless gem BO free callback

No dev->struct_mutex anywhere to be seen.

Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20200515095118.2743122-9-emil.l.velikov@gmail.com

drivers/gpu/drm/gma500/psb_drv.c

@@ -507,7 +507,7 @@ static struct drm_driver driver = {
 	.irq_uninstall = psb_irq_uninstall,
 	.irq_handler = psb_irq_handler,
 
-	.gem_free_object = psb_gem_free_object,
+	.gem_free_object_unlocked = psb_gem_free_object,
 	.gem_vm_ops = &psb_gem_vm_ops,
 
 	.dumb_create = psb_gem_dumb_create,