pinctrl: mvebu: Convert to use devm_ioremap_resource

The resource mapped by of_iomap() isn't unmapped in error path. This
patch fix the resource leakage by using devm_ioremap_resource() instead
of of_iomap().

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Reviewed-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>