ASoC: rt721-sdca: fix boost gain calculation error

Fix the boost gain calculation error in rt721_sdca_set_gain_get.
This patch is specific for "FU33 Boost Volume".

Signed-off-by: Jack Yu <jack.yu@realtek.com>
Link: https://patch.msgid.link/1b18fcde41c64d6fa85451d523c0434a@realtek.com


Signed-off-by: Mark Brown <broonie@kernel.org>