iio: adc: at91-sama5d2_adc: drop AT91_OSR_XSAMPLES defines

Drop AT91_OSR_1SAMPLES, AT91_OSR_4SAMPLES, AT91_OSR_16SAMPLES defines
and insted use their values inline.

Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220803102855.2191070-9-claudiu.beznea@microchip.com


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