Replace `sr` with `Sr`. The condition `!tmp1 || rb_is_black(tmp1)`
ensures that `tmp1` (which is `sibling->rb_right`) is either NULL
or a black node. Therefore, the right child of the sibling must be
black, and the example should use `Sr` instead of `sr`.

Signed-off-by: Chisheng Chen <johnny1001s000602@gmail.com>
---
Commit cedb08caac58 ("lib/rbtree.c: fix the example typo") stated
that the example was incorrect if `sl` and `N` did not have child
nodes, and it changed `Sr` to `sr`. However, after further review,
I do not see this issue.

 lib/rbtree.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/rbtree.c b/lib/rbtree.c
index 989c2d615f92..5114eda6309c 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -297,9 +297,9 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
 				 *   / \           / \
 				 *  N   S    -->  N   sl
 				 *     / \             \
-				 *    sl  sr            S
+				 *    sl  Sr            S
 				 *                       \
-				 *                        sr
+				 *                        Sr
 				 *
 				 * Note: p might be red, and then both
 				 * p and sl are red after rotation(which
@@ -312,9 +312,9 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
 				 *   / \            /  \
 				 *  N   sl   -->   P    S
 				 *       \        /      \
-				 *        S      N        sr
+				 *        S      N        Sr
 				 *         \
-				 *          sr
+				 *          Sr
 				 */
 				tmp1 = tmp2->rb_right;
 				WRITE_ONCE(sibling->rb_left, tmp1);
-- 
2.43.0