VS: Fix ASM_MASM support in VS >= 10

Fix a typo introduced by commit ce511435 (stringapi: Use strings for the
languages, 2014-02-03) to check the language name correctly.

Source/cmVisualStudio10TargetGenerator.cxx

@@ -1123,7 +1123,7 @@ void cmVisualStudio10TargetGenerator::WriteAllSources()
       {
       tool = "ClCompile";
       }
-    else if (lang == "ASM_NASM" &&
+    else if (lang == "ASM_MASM" &&
              this->GlobalGenerator->IsMasmEnabled())
       {
       tool = "MASM";