sysfs/cpu: Use DEVICE_ATTR_RO for nohz_full attribute

The /sys/devices/system/cpu/nohz_full file is a read-only attribute that
reports the CPUs configured for tickless operation (CONFIG_NO_HZ_FULL=y).

The current definition uses the generic DEVICE_ATTR macro, which
unnecessarily requires specifying the file mode (0444) and a NULL
store operation pointer.

This patch converts the definition to use the dedicated DEVICE_ATTR_RO
macro. This correctly expresses the read-only nature of the attribute,
removes the redundant mode field, and simplifies the code. As a related
cleanup, rename the show function from print_cpus_nohz_full() to the
standard nohz_full_show() for consistency with common sysfs attribute
naming conventions.

Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
Link: https://patch.msgid.link/20251011011830.6670-2-atomlin@atomlin.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: aarontomlin

drivers/base/cpu.c

@@ -301,12 +301,13 @@ static ssize_t print_cpus_isolated(struct device *dev,
 static DEVICE_ATTR(isolated, 0444, print_cpus_isolated, NULL);
 
 #ifdef CONFIG_NO_HZ_FULL
-static ssize_t print_cpus_nohz_full(struct device *dev,
-				    struct device_attribute *attr, char *buf)
+static ssize_t nohz_full_show(struct device *dev,
+				    struct device_attribute *attr,
+				    char *buf)
 {
 	return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(tick_nohz_full_mask));
 }
-static DEVICE_ATTR(nohz_full, 0444, print_cpus_nohz_full, NULL);
+static DEVICE_ATTR_RO(nohz_full);
 #endif
 
 #ifdef CONFIG_CRASH_HOTPLUG