opp: use list iterator only inside the loop

To move the list iterator variable into the list_for_each_entry_*()
macro in the future it should be avoided to use the list iterator
variable after the loop body.

To *never* use the list iterator variable after the loop it was
concluded to use a separate dedicated pointer variable [1].

In this case, use a new variable 'iter' as the list iterator, while
use the old variable 'new_dev' as a dedicated pointer to point to the
found entry. And BUG_ON(!new_dev);.

[1]: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

drivers/opp/debugfs.c

@@ -195,14 +195,18 @@ void opp_debug_register(struct opp_device *opp_dev, struct opp_table *opp_table)
 static void opp_migrate_dentry(struct opp_device *opp_dev,
 			       struct opp_table *opp_table)
 {
-	struct opp_device *new_dev;
+	struct opp_device *new_dev = NULL, *iter;
 	const struct device *dev;
 	struct dentry *dentry;
 
 	/* Look for next opp-dev */
-	list_for_each_entry(new_dev, &opp_table->dev_list, node)
-		if (new_dev != opp_dev)
+	list_for_each_entry(iter, &opp_table->dev_list, node)
+		if (iter != opp_dev) {
+			new_dev = iter;
 			break;
+		}
+
+	BUG_ON(!new_dev);
 
 	/* new_dev is guaranteed to be valid here */
 	dev = new_dev->dev;