tpm/st33zp24/spi: Remove useless use of memcpy.

An affectation is enough when copying 1 byte. Remove memcpy usage where
possible.

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>