KEYS: trusted: Fix TPM reservation for seal/unseal

The original patch 8c657a0 ("KEYS: trusted: Reserve TPM for seal
and unseal operations") was correct on the mailing list:

https://lore.kernel.org/linux-integrity/[email protected]/

But somehow got rebased so that the tpm_try_get_ops() in
tpm2_seal_trusted() got lost.  This causes an imbalanced put of the
TPM ops and causes oopses on TIS based hardware.

This fix puts back the lost tpm_try_get_ops()

Fixes: 8c657a0 ("KEYS: trusted: Reserve TPM for seal and unseal operations")
Reported-by: Mimi Zohar <[email protected]>
Acked-by: Mimi Zohar <[email protected]>
Signed-off-by: James Bottomley <[email protected]>

security/keys/trusted-keys/trusted_tpm2.c

@@ -79,7 +79,7 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 	if (i == ARRAY_SIZE(tpm2_hash_map))
 		return -EINVAL;
 
-	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_CREATE);
+	rc = tpm_try_get_ops(chip);
 	if (rc)
 		return rc;