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>