tpm/tpm_i2c_stm_st33: Fix coccinelle warnings. Possible NULL pointer dereference

If !client the kernel mays oops in dev_info when doing client->dev.

Reported-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>