rfid-pn532.c: Use FT_UINT24 to display complete hex value for three 3-byte fields.

Specifically: the fields are fetched as 3 bytes, but had a
 type, display of FT_UINT8, BASE_HEX so only that the LO byte was
 displayed.

Change-Id: I06ea7b9527ae788be7f19278e8ba4dc2d34b2777
Reviewed-on: https://code.wireshark.org/review/5747
Reviewed-by: maisheri <maisheri.hitesh@gmail.com>
Reviewed-by: Bill Meier <wmeier@newsguy.com>