Fix an obvious typo in an attribute's diagnostics.

Patch by Caitlin Sadowski.

Unfortunately, this attribute doesn't seem to have a single test. It is
only mentioned in comments in one test, and as a string literal in
a copy of some Clang code checked in as a test for the Indexer. =[ It
dates from 2009 r74280 as part of OpenCL 1.0.

llvm-svn: 134136

clang/lib/Sema/SemaDeclAttr.cpp

@@ -1483,7 +1483,7 @@ static void HandleReqdWorkGroupSize(Decl *D, const AttributeList &Attr,
                                     Sema &S) {
   // Attribute has 3 arguments.
   if (Attr.getNumArgs() != 3) {
-    S.Diag(Attr.getLoc(), diag::err_attribute_wrong_number_arguments) << 1;
+    S.Diag(Attr.getLoc(), diag::err_attribute_wrong_number_arguments) << 3;
     return;
   }