RDMA/hns: Fix registering dca debugfs when dca has not been set

driver inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I87LCF



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DCA debugfs is not needed when DCA is not set for this ucontext.

Fixes: a2178118 ("RDMA/hns: Add debugfs support for DCA")
Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>