tpm: Only call pm_runtime_get_sync if device has a parent

Only call pm_runtime_get_sync if the device has a parent. This
change fixes a crash in the tpm_vtpm_proxy driver since that
driver does not have a parent device.
Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

drivers/char/tpm/tpm-interface.c

@@ -357,7 +357,8 @@ ssize_t tpm_transmit(struct tpm_chip *chip, const u8 *buf, size_t bufsiz,
 	if (!(flags & TPM_TRANSMIT_UNLOCKED))
 		mutex_lock(&chip->tpm_mutex);
 
-	pm_runtime_get_sync(chip->dev.parent);
+	if (chip->dev.parent)
+		pm_runtime_get_sync(chip->dev.parent);
 
 	rc = chip->ops->send(chip, (u8 *) buf, count);
 	if (rc < 0) {
@@ -400,7 +401,8 @@ ssize_t tpm_transmit(struct tpm_chip *chip, const u8 *buf, size_t bufsiz,
 		dev_err(&chip->dev,
 			"tpm_transmit: tpm_recv: error %zd\n", rc);
 out:
-	pm_runtime_put_sync(chip->dev.parent);
+	if (chip->dev.parent)
+		pm_runtime_put_sync(chip->dev.parent);
 
 	if (!(flags & TPM_TRANSMIT_UNLOCKED))
 		mutex_unlock(&chip->tpm_mutex);