staging:iio:adc:ad7280a: Use more conservative delays to allow 105C operation.

The datasheet provides timings for operating this device at up to 105
degrees centigrade. Adopt these more conservative timings.

Suggested-by: Marcelo Schmitt <marcelo.schmitt1@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Marcelo Schmitt <marcelo.schmitt1@gmail.com>
Link: https://lore.kernel.org/r/20220206190328.333093-20-jic23@kernel.org