nvme-fabrics: allow internal passthrough command on deleting controllers

Without this we can't cleanly shut down.

Based on analysis an an earlier patch from Hannes Reinecke.

Fixes: bb06ec31 ("nvme: expand nvmf_check_if_ready checks")
Reported-by: Hannes Reinecke <hare@suse.de>
Tested-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: James Smart <james.smart@broadcom.com>