mISDN: fix possible memory leak in mISDN_dsp_element_register()

In the Linux kernel, the following vulnerability has been resolved: mISDN: fix possible memory leak in mISDN_dsp_element_register() Afer commit 1fa5ae857bb1 ("driver core: get rid of struct device's bus_id string array"), the name of device is allocated dynamically, use put_device() to give up the reference, so that the name can be freed in kobject_cleanup() when the refcount is 0. The 'entry' is going to be freed in mISDN_dsp_dev_release(), so the kfree() is removed. list_del() is called in mISDN_dsp_dev_release(), so it need be initialized.