staging: iio: adc: ad7606: fix function pointer parameter names missing.

Checkpatch.pl complains about function pointer parameter names missing.

Add parameter names.

Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Reviewed-by: Martin Kelly <mkelly@xevo.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>