USB: ch341: fix port-data memory leak

Fix port-data memory leak by moving port data allocation to port_probe
and actually implementing deallocation.

Note that this driver has never even bothered to try to deallocate it's
port data...

Compile-only tested.

Cc: <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>