Fix highp issue in lens shader on gles2

drivers/gles2/shaders/lens_distorted.glsl

@@ -1,6 +1,14 @@
 /* clang-format off */
 [vertex]
 
+#ifdef USE_GLES_OVER_GL
+#define mediump
+#define highp
+#else
+precision highp float;
+precision highp int;
+#endif
+
 attribute highp vec2 vertex; // attrib:0
 /* clang-format on */
 
@@ -20,6 +28,14 @@ void main() {
 /* clang-format off */
 [fragment]
 
+#ifdef USE_GLES_OVER_GL
+#define mediump
+#define highp
+#else
+precision mediump float;
+precision highp int;
+#endif
+
 uniform sampler2D source; //texunit:0
 /* clang-format on */