tpm: Remove useless priv field in struct tpm_vendor_specific

Remove useless priv field in struct tpm_vendor_specific and take benefit
of chip->dev.driver_data.  As priv is the latest field available in
struct tpm_vendor_specific, remove any reference to that structure.

Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>