drm/i915/gvt: Check if get_next_pt_type() always returns a valid value

According to gtt_type_table[] function get_next_pt_type() may returns
GTT_TYPE_INVALID in some cases. To prevent driver to try to create memory
page with invalid data type, additional check is added.
Signed-off-by: Aleksei Gimbitskii <aleksei.gimbitskii@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Colin Xu <colin.xu@intel.com>
Reviewed-by: Colin Xu <colin.xu@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/gtt.c

@@ -1076,6 +1076,9 @@ static struct intel_vgpu_ppgtt_spt *ppgtt_populate_spt_by_guest_entry(
 	} else {
 		int type = get_next_pt_type(we->type);
 
+		if (!gtt_type_is_pt(type))
+			goto err;
+
 		spt = ppgtt_alloc_spt_gfn(vgpu, type, ops->get_pfn(we), ips);
 		if (IS_ERR(spt)) {
 			ret = PTR_ERR(spt);