iio:adc:twl6030: Enable measurements of VUSB, VBAT and others

Some inputs need to be wired up to produce proper measurements,
without this change only near zero values are reported.

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Fixes: 1696f364 ("iio: twl6030-gpadc: TWL6030, TWL6032 GPADC driver")
Link: https://lore.kernel.org/r/20221201181635.3522962-1-andreas@kemnade.info


Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>