ppc64: Fix broken SYS V shared memory support

The initial support of the SYS V shared memory on ppc64 is broken. The call
to shmat done in the restore blob has no chance to work correctly.

This patch fixes the sys_shmat call.

Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>