x86/xen: remove redundant variable save_pud

Variable save_pud is being assigned but is never used hence it is
redundant and can be removed.

Cleans up clang warning:
variable 'save_pud' set but not used [-Wunused-but-set-variable]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>