tpm2: instead of adjusting authValue trailing 0(s), trim them as required by tpm...

tpm2: instead of adjusting authValue trailing 0(s), trim them as required by tpm spec

To keep compatibility with any existing object authValues with trailing 0's,
change tpm2_get_pin_auth() to trim trailing 0's, which is what the TPM
implementation will do. This should retain compatibility with any existing
authValues that contain trailing 0's.

Note that any existing authValues with trailing 0's are unlikely to have worked
in the way that systemd uses them in object sealing, which is as a bind key for
the encryption (and policy) session. However, it is better to be compatible
with the TPM spec (and implementations) even if previously created objects that
are affected may not have worked.

Fixes: #28414