board-grouper-panel.c: change dithering mode for better picture

from dc.c:
switch (dc->out->dither) {
 case TEGRA_DC_DISABLE_DITHER:
 	color_control |= DITHER_CONTROL_DISABLE;
        break;
 case TEGRA_DC_ORDERED_DITHER:
	color_control |= DITHER_CONTROL_ORDERED;
	break;
 case TEGRA_DC_ERRDIFF_DITHER:
	/* The line buffer for error-diffusion dither is limited
	 * to 1280 pixels per line. This limits the maximum
	 * horizontal active area size to 1280 pixels when error
	 * diffusion is enabled.
	 */
	BUG_ON(dc->mode.h_active > 1280);
	color_control |= DITHER_CONTROL_ERRDIFF;
	break;
}

so this should not introduce any problems since our panel uses
1280x800@60Hz :)

Signed-off-by: SkipXS <sskkiipp@gmail.com>