userns: fix return value on mntns_install() failure

Change return value from -EINVAL to -EPERM when the permission check fails.
Signed-off-by: Zhao Hongjiang <zhaohongjiang@huawei.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

fs/namespace.c

@@ -2775,7 +2775,7 @@ static int mntns_install(struct nsproxy *nsproxy, void *ns)
 
 	if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
 	    !nsown_capable(CAP_SYS_CHROOT))
-		return -EINVAL;
+		return -EPERM;
 
 	if (fs->users != 1)
 		return -EINVAL;