RDMA/hns: Fix unnecessary err return when using invalid congest control algorithm

Add a default congest control algorithm so that driver won't return
an error when the configured algorithm is invalid.

Fixes: f91696f2

 ("RDMA/hns: Support congestion control type selection according to the FW")
Signed-off-by: Junxian Huang <huangjunxian6@hisilicon.com>
Link: https://lore.kernel.org/r/20231028093242.670325-1-huangjunxian6@hisilicon.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>