mmc: omap_hsmmc: use devm_ioremap_resource

With devm_ioremap_resource conversion release_mem_region, iounmap can be
removed in clean up path

Signed-off-by: Balaji T K <balajitk@ti.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>