pds_core: check for work queue before use

Add a check that the wq exists before queuing up work for a
failed devcmd, as the PF is responsible for health and the VF
doesn't have a wq.

Fixes: c2dbb090 ("pds_core: health timer and workqueue")
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/20230824161754.34264-5-shannon.nelson@amd.com


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