dt-bindings: iio: hmc425a: add entry for LTC6373

The LTC6373 is a silicon, 3-bit Fully-Differential digital instrumentation
amplifier that supports the following programmable gains (Vout/Vin):
 G = 0.25, 0.5, 1, 2, 4, 8, 16 + Shutdown.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Dumitru Ceclan <mitrutzceclan@gmail.com>
Link: https://lore.kernel.org/r/20240220153553.2432-5-mitrutzceclan@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>