RDMA/rtrs: Fix some signedness bugs in error handling

The problem is that "req->sg_cnt" is an unsigned int so if "nr" is
negative, it gets type promoted to a high positive value and the condition
is false.  This patch fixes it by handling negatives separately.

Fixes: 6a98d71d ("RDMA/rtrs: client: main functionality")
Link: https://lore.kernel.org/r/20200519133223.GN2078@kadamSigned-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/ulp/rtrs/rtrs-clt.c

@@ -1047,11 +1047,10 @@ static int rtrs_map_sg_fr(struct rtrs_clt_io_req *req, size_t count)
 
 	/* Align the MR to a 4K page size to match the block virt boundary */
 	nr = ib_map_mr_sg(req->mr, req->sglist, count, NULL, SZ_4K);
-	if (unlikely(nr < req->sg_cnt)) {
 	if (nr < 0)
 		return nr;
+	if (unlikely(nr < req->sg_cnt))
 		return -EINVAL;
-	}
 	ib_update_fast_reg_key(req->mr, ib_inc_rkey(req->mr->rkey));
 
 	return nr;

drivers/infiniband/ulp/rtrs/rtrs-srv.c

@@ -649,7 +649,7 @@ static int map_cont_bufs(struct rtrs_srv_sess *sess)
 		}
 		nr = ib_map_mr_sg(mr, sgt->sgl, sgt->nents,
 				  NULL, max_chunk_size);
-		if (nr < sgt->nents) {
+		if (nr < 0 || nr < sgt->nents) {
 			err = nr < 0 ? nr : -EINVAL;
 			goto dereg_mr;
 		}