staging:iio:ad7606: fix ptr_ret.cocci warnings

drivers/staging/iio/adc/ad7606.c:357:1-3: WARNING: PTR_ERR_OR_ZERO can be used

 Use PTR_ERR_OR_ZERO rather than if(IS_ERR(...)) + PTR_ERR

Generated by: scripts/coccinelle/api/ptr_ret.cocci

CC: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/adc/ad7606.c

@@ -354,10 +354,7 @@ static int ad7606_request_gpios(struct ad7606_state *st)
 
 	st->gpio_os = devm_gpiod_get_array_optional(dev, "oversampling-ratio",
 			GPIOD_OUT_LOW);
-	if (IS_ERR(st->gpio_os))
-		return PTR_ERR(st->gpio_os);
-
-	return 0;
+	return PTR_ERR_OR_ZERO(st->gpio_os);
 }
 
 /**