Fix signed / unsigned comparison warning as error.

diff --git a/platform2/aosp/system/core/libutils/Timers.cpp b/platform2/aosp/system/core/libutils/Timers.cpp
index fd3f4a9..7a98896 100644
--- a/Timers.cpp
+++ b/Timers.cpp
@@ -28,7 +28,7 @@
 static constexpr size_t clock_id_max = 5;

 static void checkClockId(int clock) {
-    if (clock < 0 || clock >= clock_id_max) abort();
+    if (clock < 0 || clock >= static_cast<int>(clock_id_max)) abort();
 }

 #if defined(__linux__)