NFC: Fix SE discovery failure warning condition

This is a typo coming from the initial implementation. se_discover fails
when it returns something different than zero and we should only display
a warning in that case.
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

net/nfc/core.c

@@ -129,7 +129,7 @@ int nfc_dev_up(struct nfc_dev *dev)
 	/* We have to enable the device before discovering SEs */
 	if (dev->ops->discover_se) {
 		rc = dev->ops->discover_se(dev);
-		if (!rc)
+		if (rc)
 			pr_warn("SE discovery failed\n");
 	}