apparmor: fix aa_label_asxprint return check

Clang static analysis reports this issue
label.c:1802:3: warning: 2nd function call argument
  is an uninitialized value
  pr_info("%s", str);
  ^~~~~~~~~~~~~~~~~~

str is set from a successful call to aa_label_asxprint(&str, ...)
On failure a negative value is returned, not a -1.  So change
the check.

Fixes: f1bd9041 ("apparmor: add the base fns() for domain labels")
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/label.c

@@ -1744,7 +1744,7 @@ void aa_label_xaudit(struct audit_buffer *ab, struct aa_ns *ns,
 	if (!use_label_hname(ns, label, flags) ||
 	    display_mode(ns, label, flags)) {
 		len  = aa_label_asxprint(&name, ns, label, flags, gfp);
-		if (len == -1) {
+		if (len < 0) {
 			AA_DEBUG("label print error");
 			return;
 		}
@@ -1772,7 +1772,7 @@ void aa_label_seq_xprint(struct seq_file *f, struct aa_ns *ns,
 		int len;
 
 		len = aa_label_asxprint(&str, ns, label, flags, gfp);
-		if (len == -1) {
+		if (len < 0) {
 			AA_DEBUG("label print error");
 			return;
 		}
@@ -1795,7 +1795,7 @@ void aa_label_xprintk(struct aa_ns *ns, struct aa_label *label, int flags,
 		int len;
 
 		len = aa_label_asxprint(&str, ns, label, flags, gfp);
-		if (len == -1) {
+		if (len < 0) {
 			AA_DEBUG("label print error");
 			return;
 		}