Fix '+=' accumulation error when parsing numeric amounts in a format string.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@99479 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/PrintfFormatString.cpp b/lib/Analysis/PrintfFormatString.cpp
index 46acc8a..c38aae3 100644
--- a/lib/Analysis/PrintfFormatString.cpp
+++ b/lib/Analysis/PrintfFormatString.cpp
@@ -75,7 +75,7 @@
     char c = *I;
     if (c >= '0' && c <= '9') {
       hasDigits = true;
-      accumulator += (accumulator * 10) + (c - '0');
+      accumulator = (accumulator * 10) + (c - '0');
       continue;
     }