[SCSI] bfa: Use pcie_set()/get_readrq() to simplify code

Use pcie_get_readrq()/pcie_set_readrq() to simplify code.

Jon Mason proposed a similar patch a couple years ago (see below).

[bhelgaas: validate pcie_max_read_reqsz, add pointer to Jon's patch]
Reference: http://lkml.kernel.org/r/1309191190-14670-1-git-send-email-jdmason@kudzu.us


Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Jiang Liu <jiang.liu@huawei.com>
Cc: Anil Gurumurthy <agurumur@brocade.com>
Cc: Vijaya Mohan Guvva <vmohan@brocade.com>
Cc: "James E.J. Bottomley" <JBottomley@parallels.com>