Btrfs: make some volumes.c functions static

These aren't used outside of volumes.c.
Signed-off-by: NOmar Sandoval <osandov@fb.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -541,7 +541,7 @@ static void pending_bios_fn(struct btrfs_work *work)
 }
 
 
-void btrfs_free_stale_device(struct btrfs_device *cur_dev)
+static void btrfs_free_stale_device(struct btrfs_device *cur_dev)
 {
 	struct btrfs_fs_devices *fs_devs;
 	struct btrfs_device *dev;
@@ -1062,14 +1062,15 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 	return ret;
 }
 
-void btrfs_release_disk_super(struct page *page)
+static void btrfs_release_disk_super(struct page *page)
 {
 	kunmap(page);
 	put_page(page);
 }
 
-int btrfs_read_disk_super(struct block_device *bdev, u64 bytenr,
-		struct page **page, struct btrfs_super_block **disk_super)
+static int btrfs_read_disk_super(struct block_device *bdev, u64 bytenr,
+				 struct page **page,
+				 struct btrfs_super_block **disk_super)
 {
 	void *p;
 	pgoff_t index;
@@ -1811,8 +1812,8 @@ static int btrfs_check_raid_min_devices(struct btrfs_fs_info *fs_info,
 	return 0;
 }
 
-struct btrfs_device *btrfs_find_next_active_device(struct btrfs_fs_devices *fs_devs,
-					struct btrfs_device *device)
+static struct btrfs_device * btrfs_find_next_active_device(
+		struct btrfs_fs_devices *fs_devs, struct btrfs_device *device)
 {
 	struct btrfs_device *next_device;