RDMA/hns: Fix error with to_hr_hem_entries_count()

RDMA/hns: Fix error with to_hr_hem_entries_count()

For ilog2(x), if x is 0 and not a constant variable, it will return
-1. And there will be an error as below:

 hns3 0000:7d:00.0 hns_0: Local work queue 0x8 catast error, sub_event type is: 2

So modify to_hr_hem_entries_shift() to return 0 if conut is 0.

Fixes: 54d6638765b0 ("RDMA/hns: Optimize WQE buffer size calculating process")
Link: https://lore.kernel.org/r/1588931159-56875-6-git-send-email-liweihang@huawei.com
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>