hw/ppc/spapr: Make sure to close the htab_fd when migration is canceled

When canceling a migration process, we currently do not close the
HTAB migration file descriptor since htab_save_complete() is never
called in that case. So we leave the migration process with a
dangling htab_fd value around, and this causes any further migration
attempts to fail. To fix this issue, simply make sure that the
htab_fd is closed during the migration cleanup stage. And since the
cleanup() function is also called when migration succeeds, we can
also remove the call to close_htab_fd() from the htab_save_complete()
function.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1354341
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
