HID: intel-ish-hid: avoid binding wrong ishtp_cl_device

When performing a warm reset in ishtp bus driver, the ishtp_cl_device
will not be removed, its fw_client still points to the already freed
ishtp_device.fw_clients array.

Later after driver finishing ishtp client enumeration, this dangling
pointer may cause driver to bind the wrong ishtp_cl_device to the new
client, causing wrong callback to be called for messages intended for
the new client.

This helps in development of firmware where frequent switching of
firmwares is required without Linux reboot.

Signed-off-by: Hong Liu <hong.liu@intel.com>
Tested-by: Hongyan Song <hongyan.song@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/intel-ish-hid/ishtp/bus.c

@@ -675,7 +675,8 @@ int ishtp_cl_device_bind(struct ishtp_cl *cl)
 	spin_lock_irqsave(&cl->dev->device_list_lock, flags);
 	list_for_each_entry(cl_device, &cl->dev->device_list,
 			device_link) {
-		if (cl_device->fw_client->client_id == cl->fw_client_id) {
+		if (cl_device->fw_client &&
+		    cl_device->fw_client->client_id == cl->fw_client_id) {
 			cl->device = cl_device;
 			rv = 0;
 			break;
@@ -735,6 +736,7 @@ void ishtp_bus_remove_all_clients(struct ishtp_device *ishtp_dev,
 	spin_lock_irqsave(&ishtp_dev->device_list_lock, flags);
 	list_for_each_entry_safe(cl_device, n, &ishtp_dev->device_list,
 				 device_link) {
+		cl_device->fw_client = NULL;
 		if (warm_reset && cl_device->reference_count)
 			continue;