tpm: Fix fault in case CONFIG_DM_TPM is set without any TPM

In case CONFIG_DM_TPM was set without any TPM chipset configured a fault
was generated (NULL pointer access).

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
2 files changed