Update input_val for AUDIOMIX_BIT_STREAM according to latest RM.

Fixes: 6d9b8d20 ("arm64: dts: freescale: Add i.MX8MP dtsi support")
Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>