render/color: use variable instead of type in sizeof()

Conforms to the wlroots code style.

render/color.c

@@ -30,7 +30,7 @@ void wlr_color_transform_init(struct wlr_color_transform *tr, enum wlr_color_tra
 }
 
 struct wlr_color_transform *wlr_color_transform_init_srgb(void) {
-	struct wlr_color_transform *tx = calloc(1, sizeof(struct wlr_color_transform));
+	struct wlr_color_transform *tx = calloc(1, sizeof(*tx));
 	if (!tx) {
 		return NULL;
 	}

render/color_lcms2.c

@@ -95,7 +95,7 @@ struct wlr_color_transform *wlr_color_transform_init_linear_to_icc(
 		}
 	}
 
-	tx = calloc(1, sizeof(struct wlr_color_transform_lut3d));
+	tx = calloc(1, sizeof(*tx));
 	if (!tx) {
 		goto out_lcms_tr;
 	}