radeonsi: fix freeing descriptor buffers

That structure member is a pointer, so the loop with
the Elements macro only freed up the first entry.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/gallium/drivers/radeonsi/si_descriptors.c

@@ -387,7 +387,7 @@ static void si_release_buffer_resources(struct si_buffer_resources *buffers)
 {
 	int i;
 
-	for (i = 0; i < Elements(buffers->buffers); i++) {
+	for (i = 0; i < buffers->num_buffers; i++) {
 		pipe_resource_reference(&buffers->buffers[i], NULL);
 	}