audit: make symbol 'audit_nfcfgs' static

Fix sparse warnings:

kernel/auditsc.c:138:32: warning: symbol 'audit_nfcfgs' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/auditsc.c

@@ -135,7 +135,7 @@ struct audit_nfcfgop_tab {
 	const char		*s;
 };
 
-const struct audit_nfcfgop_tab audit_nfcfgs[] = {
+static const struct audit_nfcfgop_tab audit_nfcfgs[] = {
 	{ AUDIT_XT_OP_REGISTER,		"register"	},
 	{ AUDIT_XT_OP_REPLACE,		"replace"	},
 	{ AUDIT_XT_OP_UNREGISTER,	"unregister"	},