staging:iio:ad7887: Do not return error code in interrupt handler

The interrupt handler should only ever return one of the three irqreturn_t
constants and not an error code. Also make sure to always call
iio_trigger_notify_done before leaving the trigger handler.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/adc/ad7887_ring.c

@@ -82,7 +82,7 @@ static irqreturn_t ad7887_trigger_handler(int irq, void *p)
 
 	buf = kzalloc(indio_dev->scan_bytes, GFP_KERNEL);
 	if (buf == NULL)
-		return -ENOMEM;
+		goto done;
 
 	b_sent = spi_sync(st->spi, st->ring_msg);
 	if (b_sent)