Use error_code() instead of error_code::succes()

There is no std::error_code::success, so this removes much of the noise
in transitioning to std::error_code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209952 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/FileSystem.h

@@ -505,7 +505,7 @@ inline error_code file_size(const Twine &Path, uint64_t &Result) {
   if (EC)
     return EC;
   Result = Status.getSize();
-  return error_code::success();
+  return error_code();
 }
 
 /// @brief Set the file modification and access time.