iio: adc: aspeed: Replace mdelay() with fsleep() for ADC stabilization delay

iio: adc: aspeed: Replace mdelay() with fsleep() for ADC stabilization delay

The ADC stabilization delays in compensation mode and battery sensing
mode do not require atomic context. Using mdelay() here results in
unnecessary busy waiting.

Replace mdelay(1) with fsleep(1000) to allow the scheduler to run other
tasks while waiting for the ADC to stabilize.

Also fix a minor typo in the comment ("adc" -> "ADC").

Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>