iio: adc: ad7192: Simplify using devm_regulator_get_enable()

iio: adc: ad7192: Simplify using devm_regulator_get_enable()

[ Upstream commit 1ccef2e6e9205e209ad958d2e591bcca60981007 ]

Use devm_regulator_get_enable() instead of open coded get, enable,
add-action-to-disable-at-detach - pattern. Also drop the seemingly unused
struct member 'dvdd'.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://lore.kernel.org/r/9719c445c095d3d308e2fc9f4f93294f5806c41c.1660934107.git.mazziesaccount@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Stable-dep-of: 7e7dcab620cd ("iio: adc: ad7192: Correct reference voltage")
Signed-off-by: Sasha Levin <sashal@kernel.org>