nvme: Fix NULL dereference for pci nvme controllers

PCIe controllers do not have fabric opts, verify they exist before
showing ctrl_loss_tmo or reconnect_delay attributes.

Fixes: 764075fd ("nvme: expose reconnect_delay and ctrl_loss_tmo via sysfs")
Reported-by: Tobias Markus <tobias@markus-regensburg.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>