i40e: remove a stray unlock

BugLink: http://bugs.launchpad.net/bugs/1638748

commit be0cb0a upstream.

We shifted the locking around a bit but forgot to delete this unlock so
now it can unlock twice.

Fixes: cd3be16 ('i40e: Move the mutex lock in i40e_client_unregister')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/net/ethernet/intel/i40e/i40e_client.c

@@ -1009,7 +1009,6 @@ int i40e_unregister_client(struct i40e_client *client)
 	if (!i40e_client_is_registered(client)) {
 		pr_info("i40e: Client %s has not been registered\n",
 			client->name);
-		mutex_unlock(&i40e_client_mutex);
 		ret = -ENODEV;
 		goto out;
 	}