iio: adis_buffer: do not return ints in irq handlers

On an IRQ handler we should not return normal error codes as 'irqreturn_t'
is expected.

Not necessarily stable material as the old check cannot fail, so it's a bug
we can not hit.

Fixes: ccd2b52f ("staging:iio: Add common ADIS library")
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20210422101911.135630-2-nuno.sa@analog.com


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