[PATCH] rbtree_augmented: fix implicit rcu assign pointer dependency

To fix: In file included from include/linux/interval_tree_generic.h:22:0, from lib/interval_tree.c:2: include/linux/rbtree_augmented.h: In function ‘__rb_change_child_rcu’: include/linux/rbtree_augmented.h:139:4: error: implicit declaration of function ‘rcu_assign_pointer’

[PATCH] rbtree_augmented: fix implicit rcu assign pointer dependency

To fix: In file included from include/linux/interval_tree_generic.h:22:0, from lib/interval_tree.c:2: include/linux/rbtree_augmented.h: In function ‘__rb_change_child_rcu’: include/linux/rbtree_augmented.h:139:4: error: implicit declaration of function ‘rcu_assign_pointer’