powerpc: Pass a valid token to rtas_call() in phyp-dump code

ibm_configure_kernel_dump is passed as the token to rtas_call() is
never initialised.  This sets it to something sane.

Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Acked-by: Nathan Lynch <ntl@pobox.com>
Acked-by: Manish Ahuja <mahujam@gmail.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>