virSecuritySELinuxTransactionCommit: Don't mask error

In 4674fc6a I've implemented transactions for selinux driver.
Well, now that I am working in this area I've noticed a subtle
bug: @ret is initialized to 0 instead of -1. Facepalm.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NMarc Hartmayer <mhartmay@linux.ibm.com>

src/security/security_selinux.c

@@ -1091,7 +1091,7 @@ virSecuritySELinuxTransactionCommit(virSecurityManagerPtr mgr ATTRIBUTE_UNUSED,
                                     pid_t pid)
 {
     virSecuritySELinuxContextListPtr list;
-    int ret = 0;
+    int ret = -1;
 
     list = virThreadLocalGet(&contextList);
     if (!list)