dm-integrity: don't increment hash_offset twice

hash_offset is already incremented in the loop "for (i = 0; i < to_copy;
i++, ts--)". Do not increment it again.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Assisted-by: Claude:claude-opus-4.6
Fixes: 84597a44a9d8 ("dm-integrity: dm integrity: add optional discard support")
Cc: stable@vger.kernel.org