Fix GN midl template for input/output checking

An upcoming version of GN will check that inputs to scripts are generated by public dependencies of the script. The MIDL rule is the only failing part of the Windows build.

Review URL: https://codereview.chromium.org/1152743004

Cr-Commit-Position: refs/heads/master@{#332450}

build/toolchain/win/midl.gni

@@ -98,7 +98,7 @@ template("midl") {
     sources = process_file_template(invoker.sources,
                                     [ "$out_dir/$interface_identifier_file" ])
 
-    deps = [
+    public_deps = [
       ":$action_name",
     ]
   }