printk: htmldocs: add missing description

Variable and return descriptions were missing from the SRCU read
lock functions. Add them.

Signed-off-by: John Ogness <[e-mail]>
Signed-off-by: Petr Mladek <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

kernel/printk/printk.c

···
  * Use for_each_console_srcu() to iterate the console list
  *
  * Context: Any context.
+ * Return: A cookie to pass to console_srcu_read_unlock().
  */
 int console_srcu_read_lock(void)
 {
···
 /**
  * console_srcu_read_unlock - Unregister an old reader from
  *	the SRCU-protected console list
+ * @cookie: cookie returned from console_srcu_read_lock()
  *
  * Counterpart to console_srcu_read_lock()
  */