driver core: make sysfs_dev_char_kobj static

Nothing outside of drivers/base/core.c uses sysfs_dev_char_kobj, so
make it static and document what it is used for so we remember it the
next time we touch it 15 years from now.

Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230331093318.82288-7-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/base.h

@@ -191,9 +191,6 @@ const char *device_get_devnode(const struct device *dev, umode_t *mode,
 extern struct kset *devices_kset;
 void devices_kset_move_last(struct device *dev);
 
-/* /sys/dev/char directory */
-extern struct kobject *sysfs_dev_char_kobj;
-
 #if defined(CONFIG_MODULES) && defined(CONFIG_SYSFS)
 void module_add_driver(struct module *mod, struct device_driver *drv);
 void module_remove_driver(struct device_driver *drv);

drivers/base/core.c

@@ -2255,7 +2255,9 @@ static void fw_devlink_link_device(struct device *dev)
 int (*platform_notify)(struct device *dev) = NULL;
 int (*platform_notify_remove)(struct device *dev) = NULL;
 static struct kobject *dev_kobj;
-struct kobject *sysfs_dev_char_kobj;
+
+/* /sys/dev/char */
+static struct kobject *sysfs_dev_char_kobj;
 
 /* /sys/dev/block */
 static struct kobject *sysfs_dev_block_kobj;