[media] cec: rename cec_devnode fhs_lock to just lock

This lock will be used to protect more than just the fhs list.
So rename it to just 'lock'.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
diff --git a/include/media/cec.h b/include/media/cec.h
index dc7854b..fdb5d60 100644
--- a/include/media/cec.h
+++ b/include/media/cec.h
@@ -57,8 +57,8 @@
 	int minor;
 	bool registered;
 	bool unregistered;
-	struct mutex fhs_lock;
 	struct list_head fhs;
+	struct mutex lock;
 };
 
 struct cec_adapter;