Many of the older Cirrus devices share very similar code for reading the
device ID, and frequently this code is generating cppcheck warnings such
as:

sound/soc/codecs/cs42l42.c:1886:6: style: Variable 'ret' is reassigned
a value before the old one has been used. [redundantAssignment]
 ret = regmap_read(cs42l42->regmap, CS42L42_DEVID_CD, &reg);

Add a small helper function that older Cirrus devices can use to read
the device ID, which should help correct these issues.
Reported-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20210510131357.17170-2-ckeepax@opensource.cirrus.comSigned-off-by: Mark Brown <broonie@kernel.org>