RDMA/rxe: Fix compile warnings on 32-bit

Move the conditional code into a function, with two varients so it is
harder to make these kinds of mistakes.

 drivers/infiniband/sw/rxe/rxe_resp.c: In function 'atomic_write_reply':
 drivers/infiniband/sw/rxe/rxe_resp.c:794:13: error: unused variable 'payload' [-Werror=unused-variable]
   794 |         int payload = payload_size(pkt);
       |             ^~~~~~~
 drivers/infiniband/sw/rxe/rxe_resp.c:793:24: error: unused variable 'mr' [-Werror=unused-variable]
   793 |         struct rxe_mr *mr = qp->resp.mr;
       |                        ^~
 drivers/infiniband/sw/rxe/rxe_resp.c:791:19: error: unused variable 'dst' [-Werror=unused-variable]
   791 |         u64 src, *dst;
       |                   ^~~
 drivers/infiniband/sw/rxe/rxe_resp.c:791:13: error: unused variable 'src' [-Werror=unused-variable]
   791 |         u64 src, *dst;

Fixes: 034e285f ("RDMA/rxe: Make responder support atomic write on RC service")
Link: https://lore.kernel.org/linux-rdma/Y5s+EVE7eLWQqOwv@nvidia.com/Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/sw/rxe/rxe_resp.c

@@ -785,21 +785,14 @@ static enum resp_states atomic_reply(struct rxe_qp *qp,
 	return ret;
 }
 
-static enum resp_states atomic_write_reply(struct rxe_qp *qp,
+#ifdef CONFIG_64BIT
+static enum resp_states do_atomic_write(struct rxe_qp *qp,
 					struct rxe_pkt_info *pkt)
 {
-	u64 src, *dst;
-	struct resp_res *res = qp->resp.res;
 	struct rxe_mr *mr = qp->resp.mr;
 	int payload = payload_size(pkt);
+	u64 src, *dst;
 
-	if (!res) {
-		res = rxe_prepare_res(qp, pkt, RXE_ATOMIC_WRITE_MASK);
-		qp->resp.res = res;
-	}
-
-	if (!res->replay) {
-#ifdef CONFIG_64BIT
 	if (mr->state != RXE_MR_STATE_VALID)
 		return RESPST_ERR_RKEY_VIOLATION;
 
@@ -824,14 +817,29 @@ static enum resp_states atomic_write_reply(struct rxe_qp *qp,
 
 	qp->resp.opcode = pkt->opcode;
 	qp->resp.status = IB_WC_SUCCESS;
-
 	return RESPST_ACKNOWLEDGE;
+}
 #else
+static enum resp_states do_atomic_write(struct rxe_qp *qp,
+					struct rxe_pkt_info *pkt)
+{
 	return RESPST_ERR_UNSUPPORTED_OPCODE;
+}
 #endif /* CONFIG_64BIT */
+
+static enum resp_states atomic_write_reply(struct rxe_qp *qp,
+					   struct rxe_pkt_info *pkt)
+{
+	struct resp_res *res = qp->resp.res;
+
+	if (!res) {
+		res = rxe_prepare_res(qp, pkt, RXE_ATOMIC_WRITE_MASK);
+		qp->resp.res = res;
 	}
 
+	if (res->replay)
 		return RESPST_ACKNOWLEDGE;
+	return do_atomic_write(qp, pkt);
 }
 
 static struct sk_buff *prepare_ack_packet(struct rxe_qp *qp,