ARM: dts: imx6qdl-sabreauto: remove pinctrl-assert-gpios

The pinctrl-assert-gpios is an invalid pinctrl property.  It was
probably sneaked from vendor tree.  Remove it.

Fixes: 4e18a224 ("ARM: imx6qdl-sabreauto.dtsi: add max7310 support")
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>