scsi: hisi_sas: lock sensitive regions when servicing CQ interrupt

There is a bug in the current driver in that certain hisi_hba and port
structure elements which we access when servicing the CQ interrupt do
not use thread-safe accesses; these include hisi_sas_port linked-list of
active slots (hisi_sas_port.entry), bitmap of currently allocated IPTT
(in hisi_hba.slot_index_tags), and completion queue read pointer.

As a solution, lock these elements with the hisi_hba.lock.

Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Xiang Chen <chenxiang66@hisilicon.com>
Reviewed-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Tested-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>