gpio: cs5535: Switch to using managed resources with devm_

This change switches to devm_request_region to request region
and hence simplifies the module unload and does away with
release_region in remove function.

Cc: linux-gpio@vger.kernel.org
Signed-off-by: Pramod Gurav <pramod.gurav@smartplayin.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>