gl-renderer: Change 'data' type to 'uint8_t *', since 'void *' arithmetic is undefined

Signed-off-by: Raúl Peñacoba <raul.mikaop.zelda@gmail.com>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>
diff --git a/libweston/gl-renderer.c b/libweston/gl-renderer.c
index c6091af..0de2803 100644
--- a/libweston/gl-renderer.c
+++ b/libweston/gl-renderer.c
@@ -1237,7 +1237,7 @@
 	struct weston_view *view;
 	bool texture_used;
 	pixman_box32_t *rectangles;
-	void *data;
+	uint8_t *data;
 	int i, j, n;
 
 	pixman_region32_union(&gs->texture_damage,