libata: libahci: declare ahci_shost_attr_group as static

ahci_shost_attr_group is referenced only in drivers/ata/libahci.c.
Declare it as static.

Fixes: c3f69c7f ("scsi: ata: Switch to attribute groups")
Cc: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

drivers/ata/libahci.c

@@ -131,7 +131,7 @@ const struct attribute_group *ahci_shost_groups[] = {
 };
 EXPORT_SYMBOL_GPL(ahci_shost_groups);
 
-struct attribute *ahci_sdev_attrs[] = {
+static struct attribute *ahci_sdev_attrs[] = {
 	&dev_attr_sw_activity.attr,
 	&dev_attr_unload_heads.attr,
 	&dev_attr_ncq_prio_supported.attr,