iio: adis16400: do not return ints in irq handlers

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

Not necessary to apply to stable as the original check cannot fail and
as such the bug cannot actually occur.

Fixes: 5eda3550 ("staging:iio:adis16400: Preallocate transfer message")
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20210422101911.135630-3-nuno.sa@analog.com


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