NFC: nfcmrvl_uart: fix OF child-node lookup

Use the new of_get_compatible_child() helper to lookup the nfc child
node instead of using of_find_compatible_node(), which searches the
entire tree from a given start node and thus can return an unrelated
(i.e. non-child) node.

This also addresses a potential use-after-free (e.g. after probe
deferral) as the tree-wide helper drops a reference to its first
argument (i.e. the parent node).

Fixes: e097dc624f78 ("NFC: nfcmrvl: add UART driver")
Fixes: d8e018c0b321 ("NFC: nfcmrvl: update device tree bindings for Marvell NFC")
Cc: stable <[e-mail]> # 4.2
Cc: Vincent Cuissard <[e-mail]>
Cc: Samuel Ortiz <[e-mail]>
Signed-off-by: Johan Hovold <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>

drivers/nfc/nfcmrvl/uart.c

···
 	struct device_node *matched_node;
 	int ret;
 
-	matched_node = of_find_compatible_node(node, NULL, "marvell,nfc-uart");
+	matched_node = of_get_compatible_child(node, "marvell,nfc-uart");
 	if (!matched_node) {
-		matched_node = of_find_compatible_node(node, NULL,
-						       "mrvl,nfc-uart");
+		matched_node = of_get_compatible_child(node, "mrvl,nfc-uart");
 		if (!matched_node)
 			return -ENODEV;
 	}