tpm: fix checks for policy digest existence in tpm2_seal_trusted()

tpm: fix checks for policy digest existence in tpm2_seal_trusted()

BugLink: http://bugs.launchpad.net/bugs/1398274
In my original patch sealing with policy was done with dynamically
allocated buffer that I changed later into an array so the checks in
tpm2-cmd.c became invalid. This patch fixes the issue.

Fixes: 5beb0c435bdd ("keys, trusted: seal with a TPM2 authorization policy")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Acked-by: Peter Huewe <peterhuewe@gmx.de>
(cherry picked from commit f3c82ade7c59303167d56b0be3e0707751fc45e2)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>