net/mlx5: Fix crdump chunks print

Crdump repeats itself every chunk of 256bytes.
That is due to bug of missing progressing offset while copying the data
from buffer to devlink_fmsg.

Fixes: 9b1f2982 ("net/mlx5: Add support for FW fatal reporter dump")
Signed-off-by: Moshe Shemesh <moshe@mellanox.com>
Reviewed-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>