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

drivers/iio/imu/adis16400.c

@@ -645,9 +645,6 @@ static irqreturn_t adis16400_trigger_handler(int irq, void *p)
 	void *buffer;
 	int ret;
 
-	if (!adis->buffer)
-		return -ENOMEM;
-
 	if (!(st->variant->flags & ADIS16400_NO_BURST) &&
 		st->adis.spi->max_speed_hz > ADIS16400_SPI_BURST) {
 		st->adis.spi->max_speed_hz = ADIS16400_SPI_BURST;