dt-bindings: iio: light: vishay,veml6075: make vdd-supply required

dt-bindings: iio: light: vishay,veml6075: make vdd-supply required

The VEML6075 requires a single supply to operate. The property already
exists in the bindings and it is used in the example, but it is still
not on the list of required properties.

Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240223-veml6075_vdd-v1-1-ac76509b1998@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>