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>

include/linux/rbtree_augmented.h

@@ -90,7 +90,9 @@ rbname ## _rotate(struct rb_node *rb_old, struct rb_node *rb_new)	\
 	old->rbaugmented = rbcompute(old);				\
 }									\
 rbstatic const struct rb_augment_callbacks rbname = {			\
-	rbname ## _propagate, rbname ## _copy, rbname ## _rotate	\
+	.propagate = rbname ## _propagate,				\
+	.copy = rbname ## _copy,					\
+	.rotate = rbname ## _rotate					\
 };