RDMA/rtrs-srv: Init wr_cnt as 1

Fix up wr_avail accounting. if wr_cnt is 0, then we do SIGNAL for first
wr, in completion we add queue_depth back, which is not right in the
sense of tracking for available wr.

So fix it by init wr_cnt to 1.

Fixes: 9cb83748 ("RDMA/rtrs: server: main functionality")
Link: https://lore.kernel.org/r/20201217141915.56989-19-jinpu.wang@cloud.ionos.com


Signed-off-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: Gioh Kim <gi-oh.kim@cloud.ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>