NFC: digital: Call pending command callbacks at device unregister

With this patch, when freeing the command queue in the module unregister
function, the callbacks of the commands still queued are called with a
ENODEV error. This gives a chance to the command issuer to free any
memory it could have allocate.

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