tpm: check the chip reference before using it

If a driver calls tpm_dev_vendor_release for a device already released
then the driver will oops.
Signed-off-by: Andi Shyti <andi.shyti@gmail.com>
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Rajiv Andrade <srajiv@linux.vnet.ibm.com>

drivers/char/tpm/tpm.c

@@ -1330,6 +1330,9 @@ EXPORT_SYMBOL_GPL(tpm_pm_resume);
 
 void tpm_dev_vendor_release(struct tpm_chip *chip)
 {
+	if (!chip)
+		return;
+
 	if (chip->vendor.release)
 		chip->vendor.release(chip->dev);
 
@@ -1347,6 +1350,9 @@ void tpm_dev_release(struct device *dev)
 {
 	struct tpm_chip *chip = dev_get_drvdata(dev);
 
+	if (!chip)
+		return;
+
 	tpm_dev_vendor_release(chip);
 
 	chip->release(dev);