perf: arm_pmu: use DEVICE_ATTR_RO macro

Use DEVICE_ATTR_RO helper instead of plain DEVICE_ATTR,
which makes the code a bit shorter and easier to read.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20210528014130.7708-1-yuehaibing@huawei.comSigned-off-by: Will Deacon <will@kernel.org>

drivers/perf/arm_pmu.c

@@ -563,14 +563,14 @@ static int armpmu_filter_match(struct perf_event *event)
 	return ret;
 }
 
-static ssize_t armpmu_cpumask_show(struct device *dev,
-				   struct device_attribute *attr, char *buf)
+static ssize_t cpus_show(struct device *dev,
+			 struct device_attribute *attr, char *buf)
 {
 	struct arm_pmu *armpmu = to_arm_pmu(dev_get_drvdata(dev));
 	return cpumap_print_to_pagebuf(true, buf, &armpmu->supported_cpus);
 }
 
-static DEVICE_ATTR(cpus, S_IRUGO, armpmu_cpumask_show, NULL);
+static DEVICE_ATTR_RO(cpus);
 
 static struct attribute *armpmu_common_attrs[] = {
 	&dev_attr_cpus.attr,