pinctrl: digicolor: Use devm_pinctrl_register() for pinctrl registration

Use devm_pinctrl_register() for pin control registration and clean
error path.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Cc: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>