rbtree: use designated initializers

Prepare to mark sensitive kernel structures for randomization by making
sure they're using designated initializers.  These were identified
during allyesconfig builds of x86, arm, and arm64, with most initializer
fixes extracted from grsecurity.

Link: http://lkml.kernel.org/r/20161217010253.GA140470@beast
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Jie Chen <fykcee1@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/rbtree.c

@@ -427,7 +427,9 @@ static inline void dummy_copy(struct rb_node *old, struct rb_node *new) {}
 static inline void dummy_rotate(struct rb_node *old, struct rb_node *new) {}
 
 static const struct rb_augment_callbacks dummy_callbacks = {
-	dummy_propagate, dummy_copy, dummy_rotate
+	.propagate = dummy_propagate,
+	.copy = dummy_copy,
+	.rotate = dummy_rotate
 };
 
 void rb_insert_color(struct rb_node *node, struct rb_root *root)