drm/i915/gvt: Check if cur_pt_type is valid

Static code analyzer warns that index value for scratch_pt may be equal
to -1. Index value type is intel_gvt_gtt_type_t, so it may be any number
at range -1 to 17. Check first if cur_pt_type and cur_pt_type+1 is valid
values.

v2:
 - Print some error messages if page table type is invalid. (Colin Xu)

v4:
 - Print cur_pt_type in error message. (Colin Xu)

This patch fixed the critial issue #422 reported by klocwork.
Acked-by: Colin Xu <colin.xu@intel.com>
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>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

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

@@ -948,7 +948,16 @@ static int ppgtt_invalidate_spt_by_shadow_entry(struct intel_vgpu *vgpu,
 
 	if (e->type != GTT_TYPE_PPGTT_ROOT_L3_ENTRY
 		&& e->type != GTT_TYPE_PPGTT_ROOT_L4_ENTRY) {
-		cur_pt_type = get_next_pt_type(e->type) + 1;
+		cur_pt_type = get_next_pt_type(e->type);
+
+		if (!gtt_type_is_pt(cur_pt_type) ||
+				!gtt_type_is_pt(cur_pt_type + 1)) {
+			WARN(1, "Invalid page table type, cur_pt_type is: %d\n", cur_pt_type);
+			return -EINVAL;
+		}
+
+		cur_pt_type += 1;
+
 		if (ops->get_pfn(e) ==
 			vgpu->gtt.scratch_pt[cur_pt_type].page_mfn)
 			return 0;