ARM: dts: imx6qdl-kontron-samx6i: fix pwms for lcd-backlight

The pwms property have to specify the no-/inverted flag since
commit fa28d821 ("ARM: dts: imx: default to #pwm-cells = <3>
in the SoC dtsi files").

Fixes: fa28d821 ("ARM: dts: imx: default to #pwm-cells = <3> in the SoC dtsi files")
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>