ART: Add missing namespace comments

Add closing namespace comments.

Bug: 32619234
Test: m
Change-Id: I1f50e09dcd1038c4b540b87e5c19e319c1f592e4
diff --git a/compiler/optimizing/intrinsics_arm64.h b/compiler/optimizing/intrinsics_arm64.h
index 3c53517..ff59ce9 100644
--- a/compiler/optimizing/intrinsics_arm64.h
+++ b/compiler/optimizing/intrinsics_arm64.h
@@ -24,7 +24,8 @@
 
 class MacroAssembler;
 
-}}  // namespace vixl::aarch64
+}  // namespace aarch64
+}  // namespace vixl
 
 namespace art {