thermal/debugfs: Fix the NULL vs IS_ERR() confusion in debugfs_create_dir()

The debugfs_create_dir() return value is never NULL, it is either a
valid pointer or an error one.

Use IS_ERR() to check it.

Fixes: 7ef01f22 ("thermal/debugfs: Add thermal debugfs information for mitigation episodes")
Fixes: 755113d7 ("thermal/debugfs: Add thermal cooling device debugfs information")
Signed-off-by: Yang Ruibin <11162571@vivo.com>
Link: https://patch.msgid.link/20240821075934.12145-1-11162571@vivo.com
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/thermal/thermal_debugfs.c

@@ -178,11 +178,11 @@ struct thermal_debugfs {
 void thermal_debug_init(void)
 {
 	d_root = debugfs_create_dir("thermal", NULL);
-	if (!d_root)
+	if (IS_ERR(d_root))
 		return;
 
 	d_cdev = debugfs_create_dir("cooling_devices", d_root);
-	if (!d_cdev)
+	if (IS_ERR(d_cdev))
 		return;
 
 	d_tz = debugfs_create_dir("thermal_zones", d_root);
@@ -202,7 +202,7 @@ static struct thermal_debugfs *thermal_debugfs_add_id(struct dentry *d, int id)
 	snprintf(ids, IDSLENGTH, "%d", id);
 
 	thermal_dbg->d_top = debugfs_create_dir(ids, d);
-	if (!thermal_dbg->d_top) {
+	if (IS_ERR(thermal_dbg->d_top)) {
 		kfree(thermal_dbg);
 		return NULL;
 	}