btrfs: move btrfs_pinned_by_swapfile prototype into volumes.h

This is defined in volumes.c, move the prototype into volumes.h.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -560,8 +560,6 @@ struct btrfs_swapfile_pin {
 	int bg_extent_count;
 };
 
-bool btrfs_pinned_by_swapfile(struct btrfs_fs_info *fs_info, void *ptr);
-
 enum {
 	BTRFS_FS_CLOSING_START,
 	BTRFS_FS_CLOSING_DONE,

fs/btrfs/volumes.h

@@ -731,4 +731,6 @@ const char *btrfs_bg_type_to_raid_name(u64 flags);
 int btrfs_verify_dev_extents(struct btrfs_fs_info *fs_info);
 bool btrfs_repair_one_zone(struct btrfs_fs_info *fs_info, u64 logical);
 
+bool btrfs_pinned_by_swapfile(struct btrfs_fs_info *fs_info, void *ptr);
+
 #endif