fix compile error: "error: variable-sized object ‘red_data’ may not be initialized"

[movit] / invert_effect.frag

// Used only during testing. Inverts its input.
vec4 FUNCNAME(vec2 tc)
{
        vec4 rgba = INPUT(tc);
        rgba.rgb = vec3(1.0) - rgba.rgb;
        return rgba;
}