NFC: st21nfca: Change nfcid3 generation

nfcid3 is based on sensf_res value. target->sensf is never NULL
as it is a table.
Check the sensf_res_len instead to make sure sensf_res is set or not.
Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/nfc/st21nfca/st21nfca_dep.c

@@ -523,7 +523,7 @@ int st21nfca_im_send_atr_req(struct nfc_hci_dev *hdev, u8 *gb, size_t gb_len)
 	memset(atr_req->nfcid3, 0, NFC_NFCID3_MAXSIZE);
 	target = hdev->ndev->targets;
 
-	if (target->sensf_res)
+	if (target->sensf_res_len > 0)
 		memcpy(atr_req->nfcid3, target->sensf_res,
 				target->sensf_res_len);
 	else