media: atmel-isc: avoid returning a random value at isc_parse_dt()

As warned by smatch:
drivers/media/platform/atmel/atmel-isc.c:2097 isc_parse_dt() error: uninitialized symbol 'ret'.

The problem here is that of_graph_get_next_endpoint() can
potentially return NULL on its first pass, with would make
it return a random value, as ret is not initialized.

While here, use while(1) instead of for(; ;), as while is
the preferred syntax for such kind of loops.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/platform/atmel/atmel-isc.c

@@ -2039,10 +2039,10 @@ static int isc_parse_dt(struct device *dev, struct isc_device *isc)
 
 	INIT_LIST_HEAD(&isc->subdev_entities);
 
-	for (; ;) {
+	while (1) {
 		epn = of_graph_get_next_endpoint(np, epn);
 		if (!epn)
-			break;
+			return 0;
 
 		rem = of_graph_get_remote_port_parent(epn);
 		if (!rem) {