pds_core: protect devlink callbacks from fw_down state

Don't access structs that have been cleared when in the fw_down
state and the various structs have been cleaned and are waiting
to recover.  This caused a panic on rmmod when already in fw_down
and devlink_param_unregister() tried to check the parameters.

Fixes: 40ced894 ("pds_core: devlink params for enabling VIF support")
Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Reviewed-by: Brett Creeley <brett.creeley@amd.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20230824161754.34264-2-shannon.nelson@amd.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>