gl-renderer: fix double-alloc of gl_buffer_state

Obviously the first allocation is always leaked, there is a second
zalloc() right below. Fix the leak.

Found by code inspection.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

libweston/renderer-gl/gl-renderer.c

@@ -2548,7 +2548,7 @@ import_dmabuf(struct gl_renderer *gr,
 	      struct linux_dmabuf_buffer *dmabuf)
 {
 	EGLImageKHR egl_image;
-	struct gl_buffer_state *gb = zalloc(sizeof(*gb));
+	struct gl_buffer_state *gb;
 
 	if (!pixel_format_get_info(dmabuf->attributes.format))
 		return NULL;