[cogl] Apply the fix from 2c1c836417 (Flush matrix before clip planes) to GLES

glClipPlane() is affected by modelview matrix so we need to flush before
calling it.

clutter/cogl/gles/cogl.c

@@ -311,6 +311,8 @@ set_clip_plane (GLint plane_num,
   _cogl_current_matrix_rotate (angle, 0.0f, 0.0f, 1.0f);
   _cogl_current_matrix_translate (-vertex_a[0], -vertex_a[1], -vertex_a[2]);
 
+  _cogl_current_matrix_state_flush ();
+
   plane[0] = 0;
   plane[1] = -1.0;
   plane[2] = 0;