drm/vboxvideo: Replace fake VLA at end of vbva_mouse_pointer_shape with real VLA

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DEBIAN-CVE-2024-50134

In the Linux kernel, the following vulnerability has been resolved: drm/vboxvideo: Replace fake VLA at end of vbvamousepointershape with real VLA Replace the fake VLA at end of the vbvamousepointershape shape with a real VLA to fix a "memcpy: detected field-spanning write error" warning: 13.31981...