docs: dev-tools: modify SPL reference URL to actual SPL doc entry

Fix the invalid url about Semantic Patch Language

Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Link: https://lore.kernel.org/r/20220613071243.12961-1-dzm91@hust.edu.cn
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/dev-tools/coccinelle.rst

@@ -66,7 +66,7 @@ The wiki documentation always refers to the linux-next version of the script.
 
 For Semantic Patch Language(SmPL) grammar documentation refer to:
 
-http://coccinelle.lip6.fr/documentation.php
+https://coccinelle.gitlabpages.inria.fr/website/docs/main_grammar.html
 
 Using Coccinelle on the Linux kernel
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