net/mlx5: fw_tracer, Zero consumer index when reloading the tracer

When tracer is reloaded, the device will log the traces at the
beginning of the log buffer. Also, driver is reading the log buffer in
chunks in accordance to the consumer index.
Hence, zero consumer index when reloading the tracer.

Fixes: 4383cfcc

 ("net/mlx5: Add devlink reload")
Signed-off-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>