Fix MemTagSanitizer docs to point at Armv8.5-A MTE

The Memory Tagging Extension was introduced in Armv8.5-A.
diff --git a/llvm/docs/Reference.rst b/llvm/docs/Reference.rst
index 8aef4ee..9d747b8 100644
--- a/llvm/docs/Reference.rst
+++ b/llvm/docs/Reference.rst
@@ -190,7 +190,7 @@
 

 :doc:`MemTagSanitizer`

   Security hardening for production code aiming to mitigate memory

-  related vulnerabilities. Based on ARMv9 Memory Tagging Extension.

+  related vulnerabilities. Based on the Armv8.5-A Memory Tagging Extension.

 

 :doc:`Dependence Graphs <DependenceGraphs/index>`

   A description of the design of the various dependence graphs such as