Update comment to match code behavior.

llvm-svn: 233470
diff --git a/llvm/lib/MC/SubtargetFeature.cpp b/llvm/lib/MC/SubtargetFeature.cpp
index 587be54..f893104 100644
--- a/llvm/lib/MC/SubtargetFeature.cpp
+++ b/llvm/lib/MC/SubtargetFeature.cpp
@@ -82,7 +82,7 @@
 
 /// Adding features.
 void SubtargetFeatures::AddFeature(StringRef String) {
-  // Don't add empty features or features we already have.
+  // Don't add empty features.
   if (!String.empty())
     // Convert to lowercase, prepend flag if we don't already have a flag.
     Features.push_back(hasFlag(String) ? String.str() : "+" + String.lower());