iio:adc:ad_sigma_delta: Use IRQF_NO_AUTOEN rather than request and disable

These devices are not able to mask the signal used as a data ready
interrupt. As such they previously requested the irq then immediately
disabled it. Now we can avoid the potential of a spurious interrupt
by avoiding the irq being auto enabled in the first place.

I'm not sure how this code could have been called with the irq already
disabled, so I believe the conditional would always have been true and
have removed it.

Signed-off-by: Jonathan Cameron <[e-mail]>
Cc: Lars-Peter Clausen <[e-mail]>
Cc: Alexandru Ardelean <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Reviewed-by: Lars-Peter Clausen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/iio/adc/ad_sigma_delta.c

···
 	sigma_delta->trig->ops = &ad_sd_trigger_ops;
 	init_completion(&sigma_delta->completion);
 
+	sigma_delta->irq_dis = true;
 	ret = request_irq(sigma_delta->spi->irq,
 			  ad_sd_data_rdy_trig_poll,
-			  sigma_delta->info->irq_flags,
+			  sigma_delta->info->irq_flags | IRQF_NO_AUTOEN,
 			  indio_dev->name,
 			  sigma_delta);
 	if (ret)
 		goto error_free_trig;
 
-	if (!sigma_delta->irq_dis) {
-		sigma_delta->irq_dis = true;
-		disable_irq_nosync(sigma_delta->spi->irq);
-	}
 	iio_trigger_set_drvdata(sigma_delta->trig, sigma_delta);
 
 	ret = iio_trigger_register(sigma_delta->trig);