pinctrl: cygnus-mux: Use devm_pinctrl_register() for pinctrl registration

Use devm_pinctrl_register() for pin control registration.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Cc: Ray Jui <rjui@broadcom.com>
Cc: Scott Branden <sbranden@broadcom.com>
Cc: Jon Mason <jonmason@broadcom.com>
Acked-by: Ray Jui <ray.jui@broadcom.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>