mlx4_core: fix wrong comment about the reason of subtract one from the max_cqes

The reason for the pre-allocation of one CQE is to enable resizing of
the CQ.
Fix comment accordingly.
Signed-off-by: Dotan Barak <dotanb@dev.mellanox.co.il>
Signed-off-by: Eli Cohen <eli@mellanox.co.il>
Signed-off-by: Vladimir Sokolovsky <vlad@mellanox.com>
Signed-off-by: Yuval Shaia <yuval.shaia@oracle.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/main.c

@@ -514,8 +514,7 @@ static int mlx4_dev_cap(struct mlx4_dev *dev, struct mlx4_dev_cap *dev_cap)
 	dev->caps.max_rq_desc_sz     = dev_cap->max_rq_desc_sz;
 	/*
 	 * Subtract 1 from the limit because we need to allocate a
-	 * spare CQE so the HCA HW can tell the difference between an
-	 * empty CQ and a full CQ.
+	 * spare CQE to enable resizing the CQ.
 	 */
 	dev->caps.max_cqes	     = dev_cap->max_cq_sz - 1;
 	dev->caps.reserved_cqs	     = dev_cap->reserved_cqs;