Fix typo found by clang++. Yay for -Wuninitialized.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@94810 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Analysis/Analyses/PrintfFormatString.h

@@ -116,7 +116,7 @@ public:
     : start(0), hs(NotSpecified), amt(0) {}
   
   OptionalAmount(unsigned i, const char *st) 
-    : start(start), hs(Constant), amt(i) {}
+    : start(st), hs(Constant), amt(i) {}
 
   HowSpecified getHowSpecified() const { return hs; }
   bool hasDataArgument() const { return hs == Arg; }