Fix signed vs unsigned comparison.

Change-Id: I4011607858f3a82acc04509c9f795f960496ed69
diff --git a/liblog/tests/liblog_test.cpp b/liblog/tests/liblog_test.cpp
index d726f2d..24ae738 100644
--- a/liblog/tests/liblog_test.cpp
+++ b/liblog/tests/liblog_test.cpp
@@ -484,7 +484,7 @@
 
     EXPECT_EQ(true, matches);
 
-    EXPECT_LE(sizeof(max_payload_buf), max_len);
+    EXPECT_LE(sizeof(max_payload_buf), static_cast<size_t>(max_len));
 
     android_logger_list_close(logger_list);
 }