USB: serial: io_edgeport: fix use after free in debug printk

The "dev_dbg(&urb->dev->dev, ..." which happens after usb_free_urb(urb)
is a use after free of the "urb" pointer.  Store the "dev" pointer at the
start of the function to avoid this issue.

Fixes: 984f6868 ("USB: serial: io_edgeport.c: remove dbg() usage")
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Johan Hovold <johan@kernel.org>