Fix libgui warnings

The warnings were being hidden by the use of -isystem to include
frameworks/native/include.

Bug: 31752268
Test: m -j
Change-Id: Idba8278bc0a73886ecb7978617854b433c0b5875
diff --git a/libs/gui/Surface.cpp b/libs/gui/Surface.cpp
index d78a681..351d184 100644
--- a/libs/gui/Surface.cpp
+++ b/libs/gui/Surface.cpp
@@ -408,7 +408,7 @@
         timestamp = systemTime(SYSTEM_TIME_MONOTONIC);
         isAutoTimestamp = true;
         ALOGV("Surface::queueBuffer making up timestamp: %.2f ms",
-            timestamp / 1000000.f);
+            timestamp / 1000000.0);
     } else {
         timestamp = mTimestamp;
     }