tridentfb: use display information in info not in var for panning

We must not use any information in the passed var besides xoffset,
yoffset and vmode as otherwise applications might abuse it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drivers/video/tridentfb.c

@@ -987,8 +987,8 @@ static int tridentfb_pan_display(struct fb_var_screeninfo *var,
 	unsigned int offset;
 
 	debug("enter\n");
-	offset = (var->xoffset + (var->yoffset * var->xres_virtual))
-		* var->bits_per_pixel / 32;
+	offset = (var->xoffset + (var->yoffset * info->var.xres_virtual))
+		* info->var.bits_per_pixel / 32;
 	set_screen_start(par, offset);
 	debug("exit\n");
 	return 0;