clean-up EGL includes

Test: compile and run
Bug: cleanup

Change-Id: Icb6c70c80d455446d7163a20d51c41d9b6e0b578
diff --git a/opengl/libs/EGL/egl_cache.h b/opengl/libs/EGL/egl_cache.h
index 8760009..e7f1712 100644
--- a/opengl/libs/EGL/egl_cache.h
+++ b/opengl/libs/EGL/egl_cache.h
@@ -21,6 +21,7 @@
 #include <EGL/eglext.h>
 
 #include <utils/BlobCache.h>
+#include <utils/Mutex.h>
 #include <utils/String8.h>
 #include <utils/StrongPointer.h>