NFC: port100: Fix the command cancellation process

The USB out_urb used to send commands to the device can be submitted
through the standard command processing queue coming from the Digital
Protocol layer but it can also be submitted from port100_abort_cmd().

To not submit the URB while already active, a mutex is now used to
protect it and a cmd_cancel flag is used to not send command while
canceling the previous one.

Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>