ASoC: SDCA: fix the register to ctl value conversion for Q7.8 format

ASoC: SDCA: fix the register to ctl value conversion for Q7.8 format

The division calculation should be implemented using signed integer format.
This patch changes mc->shift from an unsigned type to a signed integer during the calculation.

Fixes: 501efdcb3b3a ("ASoC: SDCA: Pull the Q7.8 volume helpers out of soc-ops")
Signed-off-by: Shuming Fan <shumingf@realtek.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://patch.msgid.link/20260327082331.2277498-1-shumingf@realtek.com
Signed-off-by: Mark Brown <broonie@kernel.org>