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>
diff --git a/drivers/video/tridentfb.c b/drivers/video/tridentfb.c
index c6c7756..34cf019 100644
--- a/drivers/video/tridentfb.c
+++ b/drivers/video/tridentfb.c
@@ -987,8 +987,8 @@
 	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;