mISDN: fix misuse of put_device() in mISDN_register_device()

We should not release reference by put_device() before calling device_initialize().

Fixes: e7d1d4d9

 ("mISDN: fix possible memory leak in mISDN_register_device()")
Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>