NFC: port100: Abort current command before switching RF off

If a command is still being processed by the device, the switch RF off
command will be rejected. With this patch, the port100 driver calls
port100_abort_cmd() before sending the switch RF off command.

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