net: prestera: acl: fix return value check in prestera_acl_rule_entry_find()

rhashtable_lookup_fast() returns NULL pointer not ERR_PTR().
Return rhashtable_lookup_fast() directly to fix this.

Fixes: 47327e19

 ("net: prestera: acl: migrate to new vTCAM api")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>