tpm: fix missing migratable flag in sealing functionality for TPM2

The 'migratable' flag was not added to the key payload. This patch
fixes the problem.

Fixes: 0fe54803 ("keys, trusted: seal/unseal with TPM 2.0 chips")
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Acked-by: Peter Huewe <PeterHuewe@gmx.de>