usb: gadget: f_hid: don't call cdev_init while cdev in use

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_hid: don't call cdev_init while cdev in use When calling unbind, then bind again, cdev_init reinitialized the cdev, even though there may still be references to it. That's the case when the /dev/hidg* device is still opened. This obviously unsafe behavior like oopes. This fixes this by using cdev_alloc to put the cdev on the heap. That way, we can simply allocate a new one in hidg_bind.