RDMA/hns: Add functions to obtain netdev and bus_num from an hr_dev

driver inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7WHE3



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Add 2 inline functions to obtain netdev and bus_num from an hr_dev
to improve readability.

Signed-off-by: Junxian Huang <huangjunxian6@hisilicon.com>