video: fbdev: intelfb: use const pointer for fb_ops

Use const for fb_ops to let us make the fbops struct const in the
future.

Cc: linux-fbdev@vger.kernel.org
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/171c573bc2977a6ec374753ac7bb03a3523ca2b7.1575390740.git.jani.nikula@intel.com

drivers/video/fbdev/intelfb/intelfb.h

@@ -273,7 +273,7 @@ struct intelfb_vsync {
 
 struct intelfb_info {
 	struct fb_info *info;
-	struct fb_ops  *fbops;
+	const struct fb_ops *fbops;
 	struct pci_dev *pdev;
 
 	struct intelfb_hwstate save_state;