firmware: arm_scmi: optee: Fix missing mutex_init()

The driver allocates the mutex but not initialize it.
Use mutex_init() on it to initialize it correctly.

Link: https://lore.kernel.org/r/20211123083620.2366860-1-weiyongjun1@huawei.com
Fixes: 5f90f189 ("firmware: arm_scmi: Add optee transport")
Reported-by: NHulk Robot <hulkci@huawei.com>
Reviewed-by: NEtienne Carriere <etienne.carriere@linaro.org>
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NSudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/optee.c

@@ -506,6 +506,7 @@ static int scmi_optee_service_probe(struct device *dev)
 	agent->dev = dev;
 	agent->tee_ctx = tee_ctx;
 	INIT_LIST_HEAD(&agent->channel_list);
+	mutex_init(&agent->mu);
 
 	ret = get_capabilities(agent);
 	if (ret)