docs: networking: nfc: change block diagram to sphinx syntax

Change the block diagram to match the sphinx syntax. This will make it
possible to switch this file to rst in the future.

Signed-off-by: Robert Schwebel <r.schwebel@pengutronix.de>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
1 file changed