nvme-tcp: Fix warning with CONFIG_DEBUG_PREEMPT

We shouldn't call smp_processor_id() in a preemptible
context, but this is advisory at best, so instead
call __smp_processor_id().

Fixes: db5ad6b7 ("nvme-tcp: try to send request in queue_rq context")
Reported-by: Or Gerlitz <gerlitz.or@gmail.com>
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/tcp.c

@@ -286,7 +286,7 @@ static inline void nvme_tcp_queue_request(struct nvme_tcp_request *req,
 	 * directly, otherwise queue io_work. Also, only do that if we
 	 * are on the same cpu, so we don't introduce contention.
 	 */
-	if (queue->io_cpu == smp_processor_id() &&
+	if (queue->io_cpu == __smp_processor_id() &&
 	    sync && empty && mutex_trylock(&queue->send_mutex)) {
 		queue->more_requests = !last;
 		nvme_tcp_send_all(queue);