NFC: port100: Fix device leak

port100_probe() calls usb_get_dev(), but there is no usb_put_dev()
in port100_disconnect(). The patch adds one.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>