iio: adc: ad7476: Use mV for internal reference

iio: adc: ad7476: Use mV for internal reference

The ad7476 supports some ICs with an internal reference voltage. For
those ICs the reference voltage has been hard-coded as micro volts, but
the value which is later used in code needs to be milli volts. This
results the need to divide hard coded voltage by 1000 before using it.

Simplify code by changing the hard-coded voltage to millivolts and by
dropping the division.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Link: https://patch.msgid.link/1c26529fcc039a3ce8b5a336948229ec727ee281.1754901948.git.mazziesaccount@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>