block/rnbd-clt: Remove the unneeded result variable

Return the value from rtrs_clt_rdma_cq_direct() directly instead of
storing it in another redundant variable.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
Acked-by: Jack Wang <jinpu.wang@ionos.com>
Link: https://lore.kernel.org/r/20220824075213.221397-1-ye.xingchen@zte.com.cn
Signed-off-by: Jens Axboe <axboe@kernel.dk>