reset: fix reset_control_get_exclusive kerneldoc comment

Add missing parentheses to correctly hyperlink the reference to
reset_control_get_shared().

Fixes: 0b52297f

 ("reset: Add support for shared reset controls")
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>