[media] cec: Fix runtime BUG when (CONFIG_RC_CORE && !CEC_CAP_RC)

Currently when the RC Core is enabled (reachable) core code located
in cec_register_adapter() attempts to populate the RC structure with
a pointer to the 'parent' passed in by the caller.

Unfortunately if the caller did not specify RC capability when calling
cec_allocate_adapter(), then there will be no RC structure to populate.

This causes a "NULL pointer dereference" error.

Fixes: f51e80804f0 ("[media] cec: pass parent device in register(), not allocate()")

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Cc: <stable@vger.kernel.org>      # for v4.10 and up
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/cec/cec-core.c

@@ -304,8 +304,8 @@ int cec_register_adapter(struct cec_adapter *adap,
 	adap->devnode.dev.parent = parent;
 
 #if IS_REACHABLE(CONFIG_RC_CORE)
-	adap->rc->dev.parent = parent;
 	if (adap->capabilities & CEC_CAP_RC) {
+		adap->rc->dev.parent = parent;
 		res = rc_register_device(adap->rc);
 
 		if (res) {