dm-verity: don't crash if panic_on_corruption is not selected

If the user sets panic_on_error and doesn't set panic_on_corruption,
dm-verity should not panic on data mismatch. But, currently it panics,
because it treats data mismatch as I/O error.

This commit fixes the logic so that if there is data mismatch and
panic_on_corruption or restart_on_corruption is not selected, the system
won't restart or panic.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Fixes: f811b838 ("dm-verity: introduce the options restart_on_error and panic_on_error")