drm/etnaviv: fix gem_prime_get_sg_table to return new SG table

The object internal SG table must not be returned, as the caller
will take ownership of the returned table.

Construct a new table from the object pages and return this one
instead.
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>

drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c

@@ -23,10 +23,12 @@
 struct sg_table *etnaviv_gem_prime_get_sg_table(struct drm_gem_object *obj)
 {
 	struct etnaviv_gem_object *etnaviv_obj = to_etnaviv_bo(obj);
+	int npages = obj->size >> PAGE_SHIFT;
 
-	BUG_ON(!etnaviv_obj->sgt);  /* should have already pinned! */
+	if (WARN_ON(!etnaviv_obj->pages))  /* should have already pinned! */
+		return NULL;
 
-	return etnaviv_obj->sgt;
+	return drm_prime_pages_to_sg(etnaviv_obj->pages, npages);
 }
 
 void *etnaviv_gem_prime_vmap(struct drm_gem_object *obj)