argument: Fix clang-tidy readability-redundant-string-init
```
/home/andrew/src/openbmc/phosphor-led-sysfs/build/../argument.cpp:30:35: error: redundant string initialization [readability-redundant-string-init,-warnings-as-errors]
const std::string ArgumentParser::empty_string = "";
^~~~~~~~~~~~~~~~~
empty_string
```
Change-Id: I6b802d85b6f0ac0911e3ce85f086e8df29239f37
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/controller.cpp b/controller.cpp
index a694b3d..8219ef3 100644
--- a/controller.cpp
+++ b/controller.cpp
@@ -91,7 +91,7 @@
// Parse out Path argument.
auto path = std::move((options)["path"]);
- if (path == phosphor::led::ArgumentParser::empty_string)
+ if (path.empty())
{
ExitWithError("Path not specified.", argv);
}