migration: Add Error** argument to vmstate_save()

This will prepare ground for future changes adding an Error** argument
to qemu_savevm_state_setup().

Reviewed-by: Prasad Pandit <pjp@fedoraproject.org>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/r/20240320064911.545001-6-clg@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
1 file changed