iio: adc: ad7944: remove unused parameter

In the ad7944 driver, the ad7944_convert_and_acquire() had an unused
`chan` parameter. This patch removes the parameter.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20240524-iio-ad7944-remove-unused-parameter-v1-1-fd824d7122a0@baylibre.com


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