rpmsg: qcom: smd: Return positively when not enabled

Remoteproc treats the error codes returned from the stubbed SMD API as
errors, but the fact that SMD is not enabled should not affect
remoteproc's ability to start the remote processors.
Signed-off-by: NBjorn Andersson <bjorn.andersson@linaro.org>

include/linux/rpmsg/qcom_smd.h

@@ -18,14 +18,12 @@ static inline struct qcom_smd_edge *
 qcom_smd_register_edge(struct device *parent,
 		       struct device_node *node)
 {
-	return ERR_PTR(-ENXIO);
+	return NULL;
 }
 
 static inline int qcom_smd_unregister_edge(struct qcom_smd_edge *edge)
 {
-	/* This shouldn't be possible */
-	WARN_ON(1);
-	return -ENXIO;
+	return 0;
 }
 
 #endif