apparmor: Fix an error code in aafs_create()

We accidentally forgot to set the error code on this path.  It means we
return NULL instead of an error pointer.  I looked through a bunch of
callers and I don't think it really causes a big issue, but the
documentation says we're supposed to return error pointers here.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/apparmorfs.c

@@ -248,8 +248,10 @@ static struct dentry *aafs_create(const char *name, umode_t mode,
 
 	inode_lock(dir);
 	dentry = lookup_one_len(name, parent, strlen(name));
-	if (IS_ERR(dentry))
+	if (IS_ERR(dentry)) {
+		error = PTR_ERR(dentry);
 		goto fail_lock;
+	}
 
 	if (d_really_is_positive(dentry)) {
 		error = -EEXIST;