ggml : make gcc happy (minor)

ggml.c

@@ -1404,7 +1404,7 @@ struct ggml_context * ggml_init(struct ggml_init_params params) {
             const uint64_t t_start = ggml_time_us(); UNUSED(t_start);
 
             g_state = (struct ggml_state) {
-                /*.contexts =*/ { 0 },
+                /*.contexts =*/ { { 0 } },
             };
 
             for (int i = 0; i < GGML_MAX_CONTEXTS; ++i) {