iio: adc: spear_adc: mask SPEAR_ADC_STATUS channel and avg sample before setting...

iio: adc: spear_adc: mask SPEAR_ADC_STATUS channel and avg sample before setting register

avg sample info is a bit field coded inside the following
bits: 5,6,7 and 8 of a device status register.

Channel num info the same, but over bits: 1, 2 and 3.

Mask both values in order to avoid touching other register bits,
since the first info (avg sample), came from DT.

Signed-off-by: Rodrigo Gobbi <rodrigo.gobbi.7@gmail.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250717221559.158872-1-rodrigo.gobbi.7@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>