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>

drivers/mfd/altera-sysmgr.c

@@ -152,7 +152,7 @@ static int sysmgr_probe(struct platform_device *pdev)
 		if (!base)
 			return -ENOMEM;
 
-		sysmgr_config.max_register = res->end - res->start - 3;
+		sysmgr_config.max_register = resource_size(res) - 3;
 		regmap = devm_regmap_init_mmio(dev, base, &sysmgr_config);
 	}