nvme-tcp: fix misuse of __smp_processor_id with preemption enabled

For our pure advisory use-case, we only rely on this call as a hint, so
fix the warning complaints of using the smp_processor_id variants with
preemption enabled.

Fixes: db5ad6b7 ("nvme-tcp: try to send request in queue_rq context")
Fixes: ada83177

 ("nvme-tcp: Fix warning with CONFIG_DEBUG_PREEMPT")
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>