tpm2-util: properly load tpm2 libraries befre unsealing

tpm2-util: properly load tpm2 libraries befre unsealing

We forgot a call to dlopen_tpm2() in the unseal codepaths. As long as
automatic TPM2 device discovery was used that didn't matter, since in
that codepaths we'd have another call dlopen_tpm2(). But with an
explicitly configured TPM2 device things should work too, hence add the
missing call.

Fixes: #19206