Add missing <limits.h> include

This should fix the build for gcc 4.3.2
diff --git a/libs/surfaceflinger/SurfaceFlinger.cpp b/libs/surfaceflinger/SurfaceFlinger.cpp
index 4c719e8..554e8e7 100644
--- a/libs/surfaceflinger/SurfaceFlinger.cpp
+++ b/libs/surfaceflinger/SurfaceFlinger.cpp
@@ -23,6 +23,7 @@
 #include <fcntl.h>
 #include <errno.h>
 #include <math.h>
+#include <limits.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/ioctl.h>