nvme: make nvme_tls_attrs_group static

To suppress the compiler "warning: symbol 'nvme_tls_attrs_group' was not
declared. Should it be static?"

Fixes: 1e48b34 ("nvme: split off TLS sysfs attributes into a separate group")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/host/sysfs.c

@@ -792,7 +792,7 @@ static umode_t nvme_tls_attrs_are_visible(struct kobject *kobj,
 	return a->mode;
 }
 
-const struct attribute_group nvme_tls_attrs_group = {
+static const struct attribute_group nvme_tls_attrs_group = {
 	.attrs		= nvme_tls_attrs,
 	.is_visible	= nvme_tls_attrs_are_visible,
 };