lightnvm: Simplify config when disabled

We shouldn't compile an object file to get empty implementations;
conforms to linux coding style on conditional compilation.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index fdb4e5b..044253d 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -136,8 +136,22 @@
 int nvme_sg_io32(struct nvme_ns *ns, unsigned long arg);
 int nvme_sg_get_version_num(int __user *ip);
 
+#ifdef CONFIG_NVM
 int nvme_nvm_ns_supported(struct nvme_ns *ns, struct nvme_id_ns *id);
 int nvme_nvm_register(struct request_queue *q, char *disk_name);
 void nvme_nvm_unregister(struct request_queue *q, char *disk_name);
+#else
+static inline int nvme_nvm_register(struct request_queue *q, char *disk_name)
+{
+	return 0;
+}
+
+static inline void nvme_nvm_unregister(struct request_queue *q, char *disk_name) {};
+
+static inline int nvme_nvm_ns_supported(struct nvme_ns *ns, struct nvme_id_ns *id)
+{
+	return 0;
+}
+#endif /* CONFIG_NVM */
 
 #endif /* _NVME_H */