stm class: Do not leak the chrdev in error path

Currently, the error path of stm_register_device() forgets to unregister
the chrdev. Fix this.
Reported-by: Alan Cox <alan.cox@intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Laurent Fert <laurent.fert@intel.com>

drivers/hwtracing/stm/core.c

@@ -688,6 +688,8 @@ int stm_register_device(struct device *parent, struct stm_data *stm_data,
 	return 0;
 
 err_device:
+	unregister_chrdev(stm->major, stm_data->name);
+
 	/* matches device_initialize() above */
 	put_device(&stm->dev);
 err_free: