rculist.h: docs: Fix wrong function summary

The brief summary in the docstring for function list_next_or_null_rcu()
states that the function is supposed to provide the "first" member of a
list, whereas in truth it returns the next member.

Change the docstring so it describes what the function actually does.
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.iitr10@gmail.com>

include/linux/rculist.h

@@ -355,7 +355,7 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
 })
 
 /**
- * list_next_or_null_rcu - get the first element from a list
+ * list_next_or_null_rcu - get the next element from a list
  * @head:	the head for the list.
  * @ptr:        the list head to take the next element from.
  * @type:       the type of the struct this is embedded in.