nfc: NULL vs zero in nci_activate_target()

This is a pointer so it should be NULL instead of zero.  Sparse
complains about this stuff:
net/nfc/nci/core.c:447:37: warning: Using plain integer as NULL pointer

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c
index 12d1d4d..a47e90c 100644
--- a/net/nfc/nci/core.c
+++ b/net/nfc/nci/core.c
@@ -444,7 +444,7 @@
 {
 	struct nci_dev *ndev = nfc_get_drvdata(nfc_dev);
 	struct nci_rf_discover_select_param param;
-	struct nfc_target *target = 0;
+	struct nfc_target *target = NULL;
 	int i;
 	int rc = 0;