tpm: fix: set continueSession attribute for the unseal operation

It's better to set the continueSession attribute for the unseal
operation so that the session object is not removed as a side-effect
when the operation is successful. Since a user process created the
session, it should be also decide when the session is destroyed.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Fixes: 5beb0c43 ("keys, trusted: seal with a TPM2 authorization policy")