mfd: altera-sysmgr: Use resource_size function on resource object

drivers/mfd/altera-sysmgr.c:155:36-39: WARNING: Suspicious code. resource_size is maybe missing with res

Generated by: scripts/coccinelle/api/resource_size.cocci

Signed-off-by: Zou Wei <zou_wei@huawei.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>