reset: sti: constify of_device_id array

of_device_id is always used as const.
(See driver.of_match_table and open firmware functions)

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
Acked-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>