RDMA/rdmavt: Convert to use ERR_CAST()

As opposed to open-code, using the ERR_CAST macro clearly indicates that
this is a pointer to an error value and a type conversion was performed.
Signed-off-by: Shen Lichuan <shenlichuan@vivo.com>
Link: https://patch.msgid.link/20240828082720.33231-1-shenlichuan@vivo.comSigned-off-by: Leon Romanovsky <leon@kernel.org>

drivers/infiniband/sw/rdmavt/mr.c

@@ -348,13 +348,13 @@ struct ib_mr *rvt_reg_user_mr(struct ib_pd *pd, u64 start, u64 length,
 
 	umem = ib_umem_get(pd->device, start, length, mr_access_flags);
 	if (IS_ERR(umem))
-		return (void *)umem;
+		return ERR_CAST(umem);
 
 	n = ib_umem_num_pages(umem);
 
 	mr = __rvt_alloc_mr(n, pd);
 	if (IS_ERR(mr)) {
-		ret = (struct ib_mr *)mr;
+		ret = ERR_CAST(mr);
 		goto bail_umem;
 	}
 
@@ -542,7 +542,7 @@ struct ib_mr *rvt_alloc_mr(struct ib_pd *pd, enum ib_mr_type mr_type,
 
 	mr = __rvt_alloc_mr(max_num_sg, pd);
 	if (IS_ERR(mr))
-		return (struct ib_mr *)mr;
+		return ERR_CAST(mr);
 
 	return &mr->ibmr;
 }