dm vdo: return error on corrupted metadata in start_restoring_volume functions

The return values of VDO_ASSERT calls that validate metadata are not acted
upon.

Return UDS_CORRUPT_DATA in case of an error.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: a4eb7e25 ("dm vdo: implement the volume index")
Signed-off-by: Ivan Abramov <i.abramov@mt-integration.ru>
Reviewed-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>