RDMA/hns: Modify the mapping attribute of doorbell to device

It is more general for ARM device drivers to use the device attribute to
map PCI BAR spaces.

Fixes: 9a443537

 ("IB/hns: Add driver files for hns RoCE driver")
Link: https://lore.kernel.org/r/20211206133652.27476-1-liangwenpeng@huawei.com
Signed-off-by: Yixing Liu <liuyixing1@huawei.com>
Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>