NFC: digital: digital_tg_send_sensf_res() can be static

Fixes sparse hint:

net/nfc/digital_technology.c:640:5: sparse: symbol 'digital_tg_send_sensf_res'
was not declared. Should it be static?

Cc: Thierry Escande <thierry.escande@linux.intel.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

net/nfc/digital_technology.c

@@ -637,7 +637,7 @@ exit:
 	dev_kfree_skb(resp);
 }
 
-int digital_tg_send_sensf_res(struct nfc_digital_dev *ddev,
+static int digital_tg_send_sensf_res(struct nfc_digital_dev *ddev,
 			      struct digital_sensf_req *sensf_req)
 {
 	struct sk_buff *skb;