linux-phytec-fsl

ASoC: rsnd: Document r8a7778-specific binding

Add the missing r8a7778-specific compatible value, which is already in
use since v4.1-rc1.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@kernel.org>