cryptsetup: ignore invalid password-cache= fully

cryptsetup: ignore invalid password-cache= fully

password-cache= tracks both the cache mode and whether the option was
configured explicitly. The parser set arg_password_cache_set before
validating the value, so an invalid value was logged as ignored but
still blocked the PKCS#11 default no-cache policy.

Only mark password-cache= as configured after accepting read-only or a
valid boolean.

Repro:
build/systemd-cryptsetup attach sdscan /dev/null - \
    pkcs11-uri=auto,password-cache=bogus

Before: warned ignored, then failed with the PKCS#11 cache error.
After: warned ignored, then continued to the device check.

Follow-up for: fd8ed7f26b5e365c27599bb6b223caaaa20dd2ca