Fix google-runtime-int warnings.

Bug: 28220065
Change-Id: Ida199c66692a1638be6990d583d2ed42583fb592
diff --git a/recovery-refresh.cpp b/recovery-refresh.cpp
index 70adc70..333367e 100644
--- a/recovery-refresh.cpp
+++ b/recovery-refresh.cpp
@@ -92,7 +92,7 @@
         if (!isdigit(number.data()[0])) {
             name += ".1";
         } else {
-            unsigned long long i = std::stoull(number);
+            auto i = std::stoull(number);
             name = sub + "." + std::to_string(i + 1);
         }
     }