btrfs: use the enums instead of int type in struct btrfs_block_group fields

The 'disk_cache_state' and 'cached' fields are defined with an int type
but all the values we assigned to them come from the enums
btrfs_disk_cache_state and btrfs_caching_type. So change the type in the
btrfs_block_group structure from int to these enums - in practice an enum
is an int, so this is more for readability and clarity.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Sun YangKai <sunk67188@gmail.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/block-group.h

@@ -171,10 +171,10 @@ struct btrfs_block_group {
 	unsigned long full_stripe_len;
 	unsigned long runtime_flags;
 
-	int disk_cache_state;
+	enum btrfs_disk_cache_state disk_cache_state;
 
 	/* Cache tracking stuff */
-	int cached;
+	enum btrfs_caching_type cached;
 	struct btrfs_caching_control *caching_ctl;
 
 	struct btrfs_space_info *space_info;