manufacturingcommands: pass string by const ref

[src/manufacturingcommands.cpp:89]:
(performance) Function parameter 'setState' should be passed by const
reference.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: Ie22127f4d071d684d646d047178e639826537437
diff --git a/src/manufacturingcommands.cpp b/src/manufacturingcommands.cpp
index 5e3dbdd..31e8938 100644
--- a/src/manufacturingcommands.cpp
+++ b/src/manufacturingcommands.cpp
@@ -86,7 +86,7 @@
     return 0;
 }
 
-ipmi_ret_t ledStoreAndSet(SmSignalSet signal, std::string setState)
+ipmi_ret_t ledStoreAndSet(SmSignalSet signal, const std::string& setState)
 {
     LedProperty* ledProp = mtm.findLedProperty(signal);
     if (ledProp == nullptr)