Commit 4275f38507a4 ("OvmfPkg/AcpiPlatformDxe: alloc blobs from 64-bit
space unless restricted") introduced a variable which is [incorrectly]
identified by GCC as being potentially uninitialized. So let's just set
it to NULL before use.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>