firmware: arm_scmi: Fix double free in OPTEE transport

Channels can be shared between protocols, avoid freeing the same channel
descriptors twice when unloading the stack.

Fixes: 5f90f189 ("firmware: arm_scmi: Add optee transport")
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Tested-by: Peng Fan <peng.fan@nxp.com>  #i.MX95 19x19 EVK
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Tested-by: Florian Fainelli <florian.fainelli@broadcom.com>
Message-Id: <20240812173340.3912830-2-cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/optee.c

@@ -473,6 +473,13 @@ static int scmi_optee_chan_free(int id, void *p, void *data)
 	struct scmi_chan_info *cinfo = p;
 	struct scmi_optee_channel *channel = cinfo->transport_info;
 
+	/*
+	 * Different protocols might share the same chan info, so a previous
+	 * call might have already freed the structure.
+	 */
+	if (!channel)
+		return 0;
+
 	mutex_lock(&scmi_optee_private->mu);
 	list_del(&channel->link);
 	mutex_unlock(&scmi_optee_private->mu);