Documentation: ad4130: format list of in_voltage-voltage_filter_mode_available modes

Documentation: ad4130: format list of in_voltage-voltage_filter_mode_available modes

Sphinx reports two warnings on sysfs documentation for AD4130 driver:

Documentation/ABI/testing/sysfs-bus-iio-adc-ad4130:2: WARNING: Unexpected indentation.
Documentation/ABI/testing/sysfs-bus-iio-adc-ad4130:2: WARNING: Block quote ends without a blank line; unexpected unindent.

These are due to misformatting of sinc* modes list. Format it with bullet
list. Since each entry spans multiple lines, separate each with a blank
line.

Fixes: 62094060cf3a ("iio: adc: ad4130: add AD4130 driver")
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20221106140233.74112-1-bagasdotme@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>