ASoC: rsrc-card: tidyup convert-channels explain

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/renesas,rsrc-card.txt

@@ -30,7 +30,7 @@ Optional subnode properties:
 - frame-inversion			: bool property. Add this if the
 					  dai-link uses frame clock inversion.
 - convert-rate				: platform specified sampling rate convert
-- convert-channels			: platform specified channel size convert
+- convert-channels			: platform specified converted channel size (2 - 8 ch)
 - audio-prefix				: see audio-routing
 - audio-routing				: A list of the connections between audio components.
 					  Each entry is a pair of strings, the first being the connection's sink,