dm: pinctrl: Skip not associated gpio phandle and rise a warning message

Skip not associated gpio phandle let register the other gpios on a group.
We need anyway to send out a warning to the user to fix their uboot-board.dtsi.
Thhe handle id can be found inside the decompiled dtb

dtc -I dtb -O dts -o devicetree.dts spl/u-boot-spl.dtb

Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Reviewed-by: Simon Glass <sjg@chromium.org>