apparmor: fix error check

clang static analysis reports this representative problem:

label.c:1463:16: warning: Assigned value is garbage or undefined
        label->hname = name;
                     ^ ~~~~

In aa_update_label_name(), this the problem block of code

	if (aa_label_acntsxprint(&name, ...) == -1)
		return res;

On failure, aa_label_acntsxprint() has a more complicated return
that just -1.  So check for a negative return.

It was also noted that the aa_label_acntsxprint() main comment refers
to a nonexistent parameter, so clean up the comment.

Fixes: f1bd904 ("apparmor: add the base fns() for domain labels")
Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

Author: Tom Rix

security/apparmor/label.c

@@ -1453,7 +1453,7 @@ bool aa_update_label_name(struct aa_ns *ns, struct aa_label *label, gfp_t gfp)
 	if (label->hname || labels_ns(label) != ns)
 		return res;
 
-	if (aa_label_acntsxprint(&name, ns, label, FLAGS_NONE, gfp) == -1)
+	if (aa_label_acntsxprint(&name, ns, label, FLAGS_NONE, gfp) < 0)
 		return res;
 
 	ls = labels_set(label);
@@ -1703,7 +1703,7 @@ int aa_label_asxprint(char **strp, struct aa_ns *ns, struct aa_label *label,
 
 /**
  * aa_label_acntsxprint - allocate a __counted string buffer and print label
- * @strp: buffer to write to. (MAY BE NULL if @size == 0)
+ * @strp: buffer to write to.
  * @ns: namespace profile is being viewed from
  * @label: label to view (NOT NULL)
  * @flags: flags controlling what label info is printed