tpm: use tpm_buf in tpm_transmit_cmd() as the IO parameter

Since we pass an initialized struct tpm_buf instance in every call site
now, it is cleaner to pass that directly to the tpm_transmit_cmd() as
the TPM command/response buffer.

Fine-tune a little bit tpm_transmit() and tpm_transmit_cmd() comments
while doing this.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Reviewed-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Tested-by: Alexander Steffen <Alexander.Steffen@infineon.com>

drivers/char/tpm/tpm-sysfs.c

@@ -53,7 +53,7 @@ static ssize_t pubek_show(struct device *dev, struct device_attribute *attr,
 
 	tpm_buf_append(&tpm_buf, anti_replay, sizeof(anti_replay));
 
-	rc = tpm_transmit_cmd(chip, NULL, tpm_buf.data, PAGE_SIZE,
+	rc = tpm_transmit_cmd(chip, NULL, &tpm_buf,
 			      READ_PUBEK_RESULT_MIN_BODY_SIZE, 0,
 			      "attempting to read the PUBEK");
 	if (rc) {