[Doc] Update prefix_caching.md to match the example image (vllm-project#14420)

Signed-off-by: Louis Ulmer <[email protected]>

Author: York-RDWang

docs/source/design/v1/prefix_caching.md

@@ -221,7 +221,7 @@ In this example, we assume the block size is 4 (each block can cache 4 tokens),
 :alt: Example Time 6
 :::
 
-**Time 7: Request 2 comes in with the 33 prompt tokens, where the first 16 tokens are the same as request 0\.** Note that even the block order in the free queue was `7 - 8 - 9 - 4 - 3 - 2 - 6 - 5 - 1 - 0`, the cache hit blocks (i.e., 0, 1, 2) are touched and removed from the queue before allocation, so the free queue becomes `7 - 8 - 9 - 4 - 3 - 6 - 5`. As a result, the allocated blocks are 0 (cached), 1 (cached), 2 (cached), 7, 8, 9, 4, 3 (evicted).
+**Time 7: Request 2 comes in with the 29 prompt tokens, where the first 12 tokens are the same as request 0\.** Note that even the block order in the free queue was `7 - 8 - 9 - 4 - 3 - 2 - 6 - 5 - 1 - 0`, the cache hit blocks (i.e., 0, 1, 2) are touched and removed from the queue before allocation, so the free queue becomes `7 - 8 - 9 - 4 - 3 - 6 - 5`. As a result, the allocated blocks are 0 (cached), 1 (cached), 2 (cached), 7, 8, 9, 4, 3 (evicted).
 
 :::{image} /assets/design/v1/prefix_caching/example-time-7.png
 :alt: Example Time 7