btrfs: move btrfs_init_async_reclaim_work prototype to space-info.h

The code for this helper is in space-info.c, move the prototype to
space-info.h.
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -528,8 +528,6 @@ struct btrfs_discard_ctl {
 	atomic64_t discard_bytes_saved;
 };
 
-void btrfs_init_async_reclaim_work(struct btrfs_fs_info *fs_info);
-
 /* fs_info */
 struct reloc_control;
 struct btrfs_device;

fs/btrfs/space-info.h

@@ -158,5 +158,6 @@ static inline void btrfs_space_info_free_bytes_may_use(
 int btrfs_reserve_data_bytes(struct btrfs_fs_info *fs_info, u64 bytes,
 			     enum btrfs_reserve_flush_enum flush);
 void btrfs_dump_space_info_for_trans_abort(struct btrfs_fs_info *fs_info);
+void btrfs_init_async_reclaim_work(struct btrfs_fs_info *fs_info);
 
 #endif /* BTRFS_SPACE_INFO_H */