NFC: pn533: Staticise pn533_data_exchange()

It is not used outside this driver so no need to make the symbol global.
Signed-off-by: NAxel Lin <axel.lin@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/nfc/pn533.c

@@ -1339,7 +1339,7 @@ static int pn533_data_exchange_complete(struct pn533 *dev, void *_arg,
 	return 0;
 }
 
-int pn533_data_exchange(struct nfc_dev *nfc_dev, u32 target_idx,
+static int pn533_data_exchange(struct nfc_dev *nfc_dev, u32 target_idx,
 						struct sk_buff *skb,
 						data_exchange_cb_t cb,
 						void *cb_context)