RDMA/hns: Unify the calculation for hem index in hip08

The calculation of hem index are different between hns_roce_table_get
and hns_roce_table_find. When the table chunk size of TRRL is not
divisible by object size, it will faile to find the trrl table.

This patch is to update the calculation of the hem index in the
hns_roce_table_find to the same as which in the hns_roce_table_get.

Signed-off-by: Shaobo Xu <xushaobo2@huawei.com>
Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>