OvmfPkg/VirtioGpuDxe: Fix VS toolchain build failure
OvmfPkg/VirtioGpuDxe: Fix VS toolchain build failure

V2: add the assert codes.

Cc: Jordan Justen <a79006884ba9cf5f4f7fcbb92a15b208780d8c97@intel.com>
Cc: Laszlo Ersek <7437296077edea1cb64451c122c4dac071f0cfbc@redhat.com>
Cc: Liming Gao <6480311aeeb4b006862f6d13ebabddc03f51e507@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <1e8692d8ed8470b17e8ddd7612a0f029768dcb56@intel.com>
Reviewed-by: Laszlo Ersek <7437296077edea1cb64451c122c4dac071f0cfbc@redhat.com>
[7437296077edea1cb64451c122c4dac071f0cfbc@redhat.com: fix up subject line]
Signed-off-by: Laszlo Ersek <7437296077edea1cb64451c122c4dac071f0cfbc@redhat.com>

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