pinctrl: handle zero found dt pinconfig properties better

This adds a shortcut when no valid pinconf properties are found
in the parsed dt node, to set the values immediately and return.

Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>