iio: adc: ad7124: Enable internal reference

iio: adc: ad7124: Enable internal reference

BugLink: https://bugs.launchpad.net/bugs/1856869
commit 11d7c8d3b1259c303fb52789febed58f0bc35ad1 upstream.

When the internal reference was selected by a channel it was not enabled.
This patch fixes that and enables it.

Fixes: b3af341bbd96 ("iio: adc: Add ad7124 support")
Signed-off-by: Mircea Caprioru <mircea.caprioru@analog.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>