btrfs: rename btrfs_create_block_group_cache to btrfs_create_block_group

btrfs: rename btrfs_create_block_group_cache to btrfs_create_block_group

struct btrfs_block_group used to be called struct
btrfs_block_group_cache but got renamed to btrfs_block_group with
commit 32da5386d9a4 ("btrfs: rename btrfs_block_group_cache").

Rename btrfs_create_block_group_cache() to btrfs_create_block_group() to
reflect that change.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>