ASoC: ops: Factor out common code from get callbacks

There are only two differences between snd_soc_get_volsw() and
snd_soc_get_volsw_sx(). The maximum field is handled differently, and
snd_soc_get_volsw() supports double controls with both values in the
same register.

Factor out the common code into a new helper and pass in the
appropriate max value such that it is handled correctly for each
control.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://patch.msgid.link/20250319175123.3835849-2-ckeepax@opensource.cirrus.com


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