[PATCH] Fix comment in list.h that refers to nonexistent API

The hlist_for_each_entry_rcu() comment block refers to a nonexistent
hlist_add_rcu() API, needs to change to hlist_add_head_rcu().

Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>