reset: fix reset_control_ops kerneldoc comment

Add a missing short description to the reset_control_ops documentation.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
[p.zabel@pengutronix.de: rebased and updated commit message]
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>