st/glsl: fix silly regression finding gs/tes variants

Fixes: d19fe5e67a ("st/glsl: support clamping color outputs in compat for gs/tes")

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>

src/mesa/state_tracker/st_program.c

@@ -1641,7 +1641,7 @@ st_get_basic_variant(struct st_context *st,
 
    /* Search for existing variant */
    for (v = prog->variants; v; v = v->next) {
-      if (memcmp(&v->key, &key, sizeof(key)) == 0) {
+      if (memcmp(&v->key, key, sizeof(*key)) == 0) {
          break;
       }
    }