Input: uinput - unlock on allocation failure in ioctl

We have to unlock before returning if input_allocate_device() fails.

Fixes: 04ce40a6

 ("Input: uinput - remove uinput_allocate_device()")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>