switch to use mat4

Change-Id: I8283a989cfd2b74d53958150bc90298bc083fee7
diff --git a/services/surfaceflinger/RenderEngine/Description.h b/services/surfaceflinger/RenderEngine/Description.h
index 862301b..0230762 100644
--- a/services/surfaceflinger/RenderEngine/Description.h
+++ b/services/surfaceflinger/RenderEngine/Description.h
@@ -49,7 +49,7 @@
     // color used when texturing is disabled
     GLclampf mColor[4];
     // projection matrix
-    GLfloat mProjectionMatrix[16];
+    mat4 mProjectionMatrix;
 
 public:
     Description();
@@ -61,7 +61,7 @@
     void setTexture(const Texture& texture);
     void disableTexture();
     void setColor(GLclampf red, GLclampf green, GLclampf blue, GLclampf alpha);
-    void setProjectionMatrix(GLfloat const* mtx);
+    void setProjectionMatrix(const mat4& mtx);
 
 private:
     bool mUniformsDirty;