iio: adc: at91_adc: Use devm_request_irq() helper function

Use devm_request_irq() to request the interrupt, so we can avoid
having to manually clean this up.

Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Link: https://lore.kernel.org/r/20230828064546.2383857-2-ruanjinjie@huawei.com


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