lib/rbtree_test.c: fix uninitialized variable warning

Fix this warning:

  lib/rbtree_test.c: In function `check':
  lib/rbtree_test.c:121: warning: `blacks' may be used uninitialized in this function

Signed-off-by: Cong Ding <dinggnu@gmail.com>
Cc: Michel Lespinasse <walken@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/lib/rbtree_test.c b/lib/rbtree_test.c
index 268b239..d7f491a 100644
--- a/lib/rbtree_test.c
+++ b/lib/rbtree_test.c
@@ -118,7 +118,7 @@
 {
 	struct rb_node *rb;
 	int count = 0;
-	int blacks;
+	int blacks = 0;
 	u32 prev_key = 0;
 
 	for (rb = rb_first(&root); rb; rb = rb_next(rb)) {