media: ttusbir: avoid unnecessary usb_unlink_urb()

While the completion handler is running,
usb_unlink_urb() on yourself is a NOP. Remove it.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>