ima: Log the same audit cause whenever a file has no signature

If the file doesn't have an xattr, ima_appraise_measurement sets cause to
"missing-hash" while if there's an xattr but it's a digest instead of a
signature it sets cause to "IMA-signature-required".

Fix it by setting cause to "IMA-signature-required" in both cases.
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

security/integrity/ima/ima_appraise.c

@@ -217,7 +217,8 @@ int ima_appraise_measurement(enum ima_hooks func,
 		if (rc && rc != -ENODATA)
 			goto out;
 
-		cause = "missing-hash";
+		cause = iint->flags & IMA_DIGSIG_REQUIRED ?
+				"IMA-signature-required" : "missing-hash";
 		status = INTEGRITY_NOLABEL;
 		if (opened & FILE_CREATED)
 			iint->flags |= IMA_NEW_FILE;