lib/rbtree: get successor's color directly

After move parent assignment out, we can check the color directly.

Link: http://lkml.kernel.org/r/20191028021442.5450-2-richardw.yang@linux.intel.com
Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/rbtree_augmented.h

@@ -286,8 +286,7 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
 			rb_set_parent_color(child2, parent, RB_BLACK);
 			rebalance = NULL;
 		} else {
-			unsigned long pc2 = successor->__rb_parent_color;
-			rebalance = __rb_is_black(pc2) ? parent : NULL;
+			rebalance = rb_is_black(successor) ? parent : NULL;
 		}
 		successor->__rb_parent_color = pc;
 		tmp = successor;