UefiCpuPkg/PiSmmCpuDxeSmm: fix format string

BufferPages is UINTN, so we need "%Lu" when printing it to avoid
it being truncated.  Also cast to UINT64 to make sure it works
for 32bit builds too.

Fixes: 4f441d02 ("UefiCpuPkg/PiSmmCpuDxeSmm: fix error handling")
Reported-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>