NFC: pn544: Fix a typo in a debug message

The ending character of the string shoulb be \n, not \b.

Fixes: 17936b43

 ("NFC: Standardize logging style")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>