rcu: Fix description of kvfree_rcu()

The kvfree_rcu() header comment's description of the "ptr" parameter
is unclear, therefore rephrase it to make it clear that it is a pointer
to the memory to eventually be passed to kvfree().

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

include/linux/rcupdate.h

@@ -924,7 +924,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  *
  *     kvfree_rcu(ptr);
  *
- * where @ptr is a pointer to kvfree().
+ * where @ptr is the pointer to be freed by kvfree().
  *
  * Please note, head-less way of freeing is permitted to
  * use from a context that has to follow might_sleep()