net/mlx5: Fix pci error recovery flow

When PCI error is detected we should save the state of the pci prior to
disabling it.

Also when receiving pci slot reset call we need to verify that the
device is responsive.

Fixes: 89d44f0a ('net/mlx5_core: Add pci error handlers to mlx5_core
driver')
Signed-off-by: Mohamad Haj Yahia <mohamad@mellanox.com>

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>