btrfs: rename btrfs_block_group_cache

The type name is misleading, a single entry is named 'cache' while this
normally means a collection of objects. Rename that everywhere. Also the
identifier was quite long, making function prototypes harder to format.

Suggested-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index a1da1f4..5ebbe8a 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -397,7 +397,7 @@ static ssize_t raid_bytes_show(struct kobject *kobj,
 
 {
 	struct btrfs_space_info *sinfo = to_space_info(kobj->parent);
-	struct btrfs_block_group_cache *block_group;
+	struct btrfs_block_group *block_group;
 	int index = btrfs_bg_flags_to_raid_index(to_raid_kobj(kobj)->flags);
 	u64 val = 0;
 
@@ -861,7 +861,7 @@ static void init_feature_attrs(void)
  * Create a sysfs entry for a given block group type at path
  * /sys/fs/btrfs/UUID/allocation/data/TYPE
  */
-void btrfs_sysfs_add_block_group_type(struct btrfs_block_group_cache *cache)
+void btrfs_sysfs_add_block_group_type(struct btrfs_block_group *cache)
 {
 	struct btrfs_fs_info *fs_info = cache->fs_info;
 	struct btrfs_space_info *space_info = cache->space_info;