RDMA/rtrs-srv: fix SG mapping

RDMA/rtrs-srv: fix SG mapping

This fixes the following error on the server side:

   RTRS server session allocation failed: -EINVAL

caused by the caller of the `ib_dma_map_sg()`, which does not expect
less mapped entries, than requested, which is in the order of things
and can be easily reproduced on the machine with enabled IOMMU.

The fix is to treat any positive number of mapped sg entries as a
successful mapping and cache DMA addresses by traversing modified
SG table.

Fixes: 9cb837480424 ("RDMA/rtrs: server: main functionality")
Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Grzegorz Prajsner <grzegorz.prajsner@ionos.com>
Link: https://patch.msgid.link/20260107161517.56357-2-haris.iqbal@ionos.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>