iio: adc: at91-sama5d2_adc: remove unused definition

Remove unused register definition
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Link: https://lore.kernel.org/r/20210901123013.329792-4-eugen.hristev@microchip.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/at91-sama5d2_adc.c

@@ -143,8 +143,6 @@
 #define AT91_SAMA5D2_COR	0x4c
 #define AT91_SAMA5D2_COR_DIFF_OFFSET	16
 
-/* Channel Data Register 0 */
-#define AT91_SAMA5D2_CDR0	0x50
 /* Analog Control Register */
 #define AT91_SAMA5D2_ACR	0x94
 /* Analog Control Register - Pen detect sensitivity mask */