wcn36xx: fix iris child-node lookup

Fix child-node lookup during probe, which ended up searching the whole
device tree depth-first starting at the parent rather than just matching
on its children.

To make things worse, the parent mmio node was also prematurely freed.

Fixes: fd52bdae9a ("wcn36xx: Disable 5GHz for wcn3620")
Cc: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/wcn36xx/main.c

@@ -1233,7 +1233,7 @@ static int wcn36xx_platform_get_resources(struct wcn36xx *wcn,
 	}
 
 	/* External RF module */
-	iris_node = of_find_node_by_name(mmio_node, "iris");
+	iris_node = of_get_child_by_name(mmio_node, "iris");
 	if (iris_node) {
 		if (of_device_is_compatible(iris_node, "qcom,wcn3620"))
 			wcn->rf_id = RF_IRIS_WCN3620;