RDMA/rtrs: Add error messages for failed operations.

It could help debugging in case of error happens.

Link: https://lore.kernel.org/r/20210712060750.16494-2-jinpu.wang@ionos.com


Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Reviewed-by: Aleksei Marov <aleksei.marov@ionos.com>
Reviewed-by: Gioh Kim <gi-oh.kim@ionos.com>
Reviewed-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>