btrfs: make btrfs_free_device() static

The function btrfs_free_device() is never used outside of volumes.c, so
make it static and remove its prototype declaration at volumes.h.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -391,7 +391,7 @@ static struct btrfs_fs_devices *alloc_fs_devices(const u8 *fsid,
 	return fs_devs;
 }
 
-void btrfs_free_device(struct btrfs_device *device)
+static void btrfs_free_device(struct btrfs_device *device)
 {
 	WARN_ON(!list_empty(&device->post_commit_list));
 	rcu_string_free(device->name);

fs/btrfs/volumes.h

@@ -617,7 +617,6 @@ struct btrfs_device *btrfs_alloc_device(struct btrfs_fs_info *fs_info,
 					const u64 *devid, const u8 *uuid,
 					const char *path);
 void btrfs_put_dev_args_from_path(struct btrfs_dev_lookup_args *args);
-void btrfs_free_device(struct btrfs_device *device);
 int btrfs_rm_device(struct btrfs_fs_info *fs_info,
 		    struct btrfs_dev_lookup_args *args,
 		    struct block_device **bdev, fmode_t *mode);