[mlir:bazel] Fix build broken by #169670.

This PR adds a dependency to the `BUILD` files overlay silently added by
 ##169670.

Signed-off-by: Ingo Müller <[email protected]>

Author: ingomueller-net

utils/bazel/llvm-project-overlay/mlir/BUILD.bazel

@@ -10118,6 +10118,7 @@ cc_binary(
         "//llvm:TableGen",
         "//llvm:TargetParser",
         "//llvm:config",
+        "//llvm:vt_gen",
     ],
 )