RDMA/erdma: Unify the names related to doorbell records

There exist two different names for the doorbell records: db_info and
db_record. We use dbrec for cpu address of the doorbell record and
dbrec_dma for dma address of the doorbell recordi uniformly.

Reviewed-by: Cheng Xu <chengyou@linux.alibaba.com>
Signed-off-by: Boshi Yu <boshiyu@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240311113821.22482-3-boshiyu@alibaba-inc.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>