i915: put ARX back into index mode before doing restore

Fixes resume from hibernate in some configurations.

linux-core/i915_drv.c

@@ -247,6 +247,7 @@ static void i915_restore_vga(struct drm_device *dev)
 			   dev_priv->saveGR[0x18]);
 
 	/* Attribute controller registers */
+	inb(st01); /* switch back to index mode */
 	for (i = 0; i < 20; i++)
 		i915_write_ar(st01, i, dev_priv->saveAR[i], 0);
 	inb(st01); /* switch back to index mode */