net/mlx5: Fix FW tracer timestamp calculation

[ Upstream commit 61db3d7b99a367416e489ccf764cc5f9b00d62a1 ]

Fix a bug in calculation of FW tracer timestamp. Decreasing one in the
calculation should effect only bits 52_7 and not effect bits 6_0 of the
timestamp, otherwise bits 6_0 are always set in this calculation.

Fixes: 70dd6fdb ("net/mlx5: FW tracer, parse traces and kernel tracing support")
Signed-off-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Feras Daoud <ferasda@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>