dt-bindings: iio: adc: ad7380: add support for ad738x-4 4 channels variants

Add compatible support for ad7380/1/3/4-4 parts which are 4 channels
variants from ad7380/1/3/4

Signed-off-by: Julien Stephan <jstephan@baylibre.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240528-adding-new-ad738x-driver-v7-6-4cd70a4c12c8@baylibre.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>