firmware: arm_scmi: Remove duplicate declaration of struct scmi_protocol_handle

struct scmi_protocol_handle is declared twice, let us remove the duplicate
declaration.

Link: https://lore.kernel.org/r/20210427033031.4580-1-wanjiabing@vivo.comReviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
[sudeep.holla: minor updates to the title and the changelog]
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/notify.h

@@ -79,8 +79,6 @@ struct scmi_protocol_events {
 
 int scmi_notification_init(struct scmi_handle *handle);
 void scmi_notification_exit(struct scmi_handle *handle);
-
-struct scmi_protocol_handle;
 int scmi_register_protocol_events(const struct scmi_handle *handle, u8 proto_id,
 				  const struct scmi_protocol_handle *ph,
 				  const struct scmi_protocol_events *ee);