iio: amplifier: hmc425a: simplify using devm_regulator_get_enable()

iio: amplifier: hmc425a: simplify using devm_regulator_get_enable()

Drop open-coded pattern: 'devm_regulator_get(), regulator_enable(),
add_action_or_reset(regulator_disable)' and use the
devm_regulator_get_enable() and drop the pointer to the regulator.
This simplifies code and makes it less tempting to add manual control
for the regulator which is also controlled by devm.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/8b1193fdefb231a6d721e2bded52c48e56039c20.1660934107.git.mazziesaccount@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>