mlx5core: Don't query the PCI config space for offline during a firmware command.

Querying the PCI config space for offline for every firmware command blocks
the PCI bus and affects performance. Especially for packet pacing and TLS
when objects are frequently created and destroyed.

Reviewed by: kib
Sponsored by: Mellanox Technologies // NVIDIA Networking

(cherry picked from commit e787b5acb1bdf97fc04ec3ebebb7a8dd40d85199)