ASoC: omap-hdmi-audio: Fix invalid combination of DM_INH and CA

DM_INH = 1 (stereo downmix prohibited) and CA = 0x00 (Channel
Allocation: FR, FL) is an invalid combination according to the
HDMI Compliance Test 7.31 "Audio InfoFrame".

Signed-off-by: Misael Lopez Cruz <misael.lopez@ti.com>
Signed-off-by: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Mark Brown <broonie@kernel.org>