iio: adc: at91-sama5d2_adc: lock around at91_adc_read_info_raw()

Remove iio_device_{claim, release}_direct_mode() and lock/unlock to
&st->lock from at91_adc_read_info_raw(). Instead add a wrapper around
at91_adc_read_info_raw() and do there the lock/unlock. This will allow
using the at91_adc_read_info_raw() in patch that add support for
temperature sensor.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220803102855.2191070-16-claudiu.beznea@microchip.com


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