Use size_t instead of int for integer_sequence.size()

Also skip an unnecessary value initialization.

Bug: 160010896
Test: atest libinput_tests
Change-Id: Ibe4dfc587f3cba9ed2ebd5e9ff95f771bf571123
diff --git a/include/input/Flags.h b/include/input/Flags.h
index f43829f..4ad9056 100644
--- a/include/input/Flags.h
+++ b/include/input/Flags.h
@@ -68,10 +68,10 @@
 
 template <typename F, typename T, T... I>
 constexpr auto generate_flag_values(std::integer_sequence<T, I...> seq) {
-    constexpr int count = seq.size();
+    constexpr size_t count = seq.size();
 
     std::array<F, count> values{};
-    for (int i = 0, v = 0; v < count; ++i) {
+    for (size_t i = 0, v = 0; v < count; ++i) {
         values[v++] = static_cast<F>(T{1} << i);
     }