IB/mlx5: Use unlimited rate when static rate is not supported

Before the change, if the user passed a static rate value different
than zero and the FW doesn't support static rate,
it would end up configuring rate of 2.5 GBps.

Fix this by using rate 0; unlimited, in cases where FW
doesn't support static rate configuration.

Cc: <stable@vger.kernel.org> # 3.10
Fixes: e126ba97 ("mlx5: Add driver for Mellanox Connect-IB adapters")
Reviewed-by: Majd Dibbiny <majd@mellanox.com>
Signed-off-by: Danit Goldberg <danitg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/qp.c

@@ -2455,18 +2455,18 @@ enum {
 
 static int ib_rate_to_mlx5(struct mlx5_ib_dev *dev, u8 rate)
 {
-	if (rate == IB_RATE_PORT_CURRENT) {
+	if (rate == IB_RATE_PORT_CURRENT)
 		return 0;
-	} else if (rate < IB_RATE_2_5_GBPS || rate > IB_RATE_300_GBPS) {
+
+	if (rate < IB_RATE_2_5_GBPS || rate > IB_RATE_300_GBPS)
 		return -EINVAL;
-	} else {
-		while (rate != IB_RATE_2_5_GBPS &&
+
+	while (rate != IB_RATE_PORT_CURRENT &&
 	       !(1 << (rate + MLX5_STAT_RATE_OFFSET) &
 		 MLX5_CAP_GEN(dev->mdev, stat_rate_support)))
 		--rate;
-	}
 
-	return rate + MLX5_STAT_RATE_OFFSET;
+	return rate ? rate + MLX5_STAT_RATE_OFFSET : rate;
 }
 
 static int modify_raw_packet_eth_prio(struct mlx5_core_dev *dev,