st/vega: Fix OpenVG demo segfaults.

When the paint is color, paint_bind_samplers binds a dummy sampler
without a texture.  It causes demos requiring a sampler (those use a
mask or an image) to crash.

src/gallium/state_trackers/vega/paint.c

@@ -639,9 +639,6 @@ VGint paint_bind_samplers(struct vg_paint *paint, struct pipe_sampler_state **sa
    }
       break;
    default:
-      samplers[0] = &paint->pattern.sampler; /* dummy */
-      textures[0] = 0;
-      return 0;
       break;
    }
    return 0;