[IA64] fix GNTTABOP_replace_and_unmap

[IA64] fix GNTTABOP_replace_and_unmap

This patch fixes the following xen panic repored by Akio Takebe.
> When we tested network between domU <-> dom0 with FTP load tools,
> we hitted BUG() in hypervisor. It is always reproducible for a few minutes.
> At that time, we got the following message.
> vmi15.sky.yk.fujitsu.co.jp login: (XEN) Xen BUG at mm.c:1254
>
> (XEN) FIXME: implement ia64 dump_execution_state()
> (XEN)
> (XEN) ****************************************
> (XEN) Panic on CPU 0:
> (XEN) Xen BUG at mm.c:1254
> (XEN) ****************************************
> (XEN)
> (XEN) Manual reset required ('noreboot' specified)
> (XEN) machine_halt called.  spinning...

GNTTABOP_replace_and_unmap must updates both the p2m table and m2p
table. However the m2p table update was missing so that
the above BUG_ON() was triggered detecting the inconsistency
between the p2m table and the m2p table.
This patch adds the missing the m2p table updates.
This patch also fixes the error path of the function. It may
return before completing the page table manipulation.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>