reset: sti: reset-syscfg: fix struct description warnings

Fix formating of struct description to avoid warning highlighted
by W=1 compilation.

Fixes: e5d76075 ("drivers: reset: STi SoC system configuration reset controller support")
Signed-off-by: Alain Volmat <avolmat@me.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>