Fix a comment bug in toascii simplifier

When I migrated the toascii simplifier in r168580 Benjamin Kramer noticed
a bug in one of the comments that I migrated.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168605 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/SimplifyLibCalls.cpp

@@ -1315,7 +1315,7 @@ struct ToAsciiOpt : public LibCallOptimization {
         !FT->getParamType(0)->isIntegerTy(32))
       return 0;
 
-    // isascii(c) -> c & 0x7f
+    // toascii(c) -> c & 0x7f
     return B.CreateAnd(CI->getArgOperand(0),
                        ConstantInt::get(CI->getType(),0x7F));
   }