RDMA/rtrs-srv: Clean up the code in __rtrs_srv_change_state

No need to use double switch to check the change of state everywhere,
let's change them to "if" to reduce size.

Link: https://lore.kernel.org/r/20210528113018.52290-5-jinpu.wang@ionos.com


Signed-off-by: Guoqing Jiang <guoqing.jiang@ionos.com>
Reviewed-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>