drm/i915/gvt: Refine error handling for intel_vgpu_pin_mm

When it is failed in shadow_mm, the pin_count should rollback
to the original states before return.

v2:
- split the mixed several error paths for better review. (Zhenyu)

v3:
  increase the pincount after shadow success. (Zhenyu)
Signed-off-by: fred gao <fred.gao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

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

@@ -1647,14 +1647,13 @@ int intel_vgpu_pin_mm(struct intel_vgpu_mm *mm)
 	if (WARN_ON(mm->type != INTEL_GVT_MM_PPGTT))
 		return 0;
 
-	atomic_inc(&mm->pincount);
-
 	if (!mm->shadowed) {
 		ret = shadow_mm(mm);
 		if (ret)
 			return ret;
 	}
 
+	atomic_inc(&mm->pincount);
 	list_del_init(&mm->lru_list);
 	list_add_tail(&mm->lru_list, &mm->vgpu->gvt->gtt.mm_lru_list_head);
 	return 0;