leds: lm3692x: Use flags from LM3692X_BOOST_CTRL

The current setup of LM3692X_BOOST_CTRL uses flags from LM3692X_BRT_CTRL.
Use flags from LM3692X_BOOST_CTRL but leave the resulting register value
unchanged.

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Reviewed-by: Dan Murphy <dmurphy@ti.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Pavel Machek <pavel@ucw.cz>