tpm/tpm_i2c_stm_st33: Replace err/rc/ret by ret for a function return code

Some functions return err, rc or ret for a status code.

Return ret instead for all of them.

Reviewed-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>