net/mlx5: FWTrace, cancel work on alloc pd error flow

Handle error flow on mlx5_core_alloc_pd() failure,
read_fw_strings_work must be canceled.

Fixes: c71ad41c ("net/mlx5: FW tracer, events handling")
Reported-by: Pavel Machek (CIP) <pavel@denx.de>
Suggested-by: Pavel Machek (CIP) <pavel@denx.de>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Aya Levin <ayal@nvidia.com>