WPS: Use pre-configured NFC password token instead of overriding it

WPS: Use pre-configured NFC password token instead of overriding it

"WPS_NFC_TOKEN <WPS/NDEF>" used to generate a new NFC password token
regardless of whether there was a pre-configured token in the
configuration. Change this to use the pre-configured value, if
available, instead. This allows the same command to be used to write the
password token to an NFC tag more conveniently.

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>