netfilter: Remove unnecessary conversion to bool

Here we could use the '!=' expression to fix the following coccicheck
warning:

./net/netfilter/xt_nfacct.c:30:41-46: WARNING: conversion to bool not needed here
Reported-by: Tosk Robot <tencent_os_robot@tencent.com>
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/xt_nfacct.c

@@ -27,7 +27,7 @@ static bool nfacct_mt(const struct sk_buff *skb, struct xt_action_param *par)
 
 	overquota = nfnl_acct_overquota(xt_net(par), info->nfacct);
 
-	return overquota == NFACCT_UNDERQUOTA ? false : true;
+	return overquota != NFACCT_UNDERQUOTA;
 }
 
 static int