ArmVirtPkg/PlatformPeiLib: add dummy assignment to work around older GCC

ArmVirtPkg/PlatformPeiLib: add dummy assignment to work around older GCC

Older GCC (<= 4.9) fail to infer that Parent is never used unless it
has been assigned before, and may throw an error like

  /work/git/edk2/ArmVirtPkg/Library/PlatformPeiLib/PlatformPeiLib.c:
      In function ‘PlatformPeim’:
  /work/git/edk2/ArmVirtPkg/Library/PlatformPeiLib/PlatformPeiLib.c:132:24:
      error: ‘Parent’ may be used uninitialized in this function
                                                [-Werror=maybe-uninitialized]
             RangesProp = fdt_getprop (Base, Parent, "ranges", &RangesLen);

Set Parent to 0 at the start of the sequence to work around this.

Link: https://bugzilla.tianocore.org/show_bug.cgi?id=2601
Fixes: 82662a3b5f56e974 ("ArmVirtPkg/PlatformPeiLib: discover the TPM base ...")
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>