ASoC: sun4i-codec: Add "Right Mixer" to "Line Out Mono Diff." route

The mono differential output for "Line Out" downmixes the stereo audio
from the mixer, instead of just taking the left channel.

Add a route from the "Right Mixer" to "Line Out Source Playback Route"
through the "Mono Differential" path, so DAPM doesn't shut down
everything if the left channel is muted.

Fixes: 0f909f9 ("ASoC: sun4i-codec: Add support for A31 Line Out
		      playback")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sunxi/sun4i-codec.c

@@ -1058,6 +1058,7 @@ static const struct snd_soc_dapm_route sun6i_codec_codec_dapm_routes[] = {
 	{ "Line Out Source Playback Route", "Stereo", "Left Mixer" },
 	{ "Line Out Source Playback Route", "Stereo", "Right Mixer" },
 	{ "Line Out Source Playback Route", "Mono Differential", "Left Mixer" },
+	{ "Line Out Source Playback Route", "Mono Differential", "Right Mixer" },
 	{ "LINEOUT", NULL, "Line Out Source Playback Route" },
 
 	/* ADC Routes */