iio:inkern: fix overwritten -EPROBE_DEFER in of_iio_channel_get_by_name

Fixes: a2c12493 ('iio: of_iio_channel_get_by_name() returns non-null pointers for error legs')

which improperly assumes that of_iio_channel_get_by_name must always
return NULL and thus now hides -EPROBE_DEFER.
Signed-off-by: Johannes Pointner <johannes.pointner@br-automation.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Cc: Stable@vger.kernel.org

drivers/iio/inkern.c

@@ -178,7 +178,7 @@ static struct iio_channel *of_iio_channel_get_by_name(struct device_node *np,
 			index = of_property_match_string(np, "io-channel-names",
 							 name);
 		chan = of_iio_channel_get(np, index);
-		if (!IS_ERR(chan))
+		if (!IS_ERR(chan) || PTR_ERR(chan) == -EPROBE_DEFER)
 			break;
 		else if (name && index >= 0) {
 			pr_err("ERROR: could not get IIO channel %s:%s(%i)\n",