btrfs-progs: fix using on-disk structure to store in memory data

btrfs-progs: fix using on-disk structure to store in memory data

In 'qgroup_count' structure 'diskinfo' and 'info' are used to store only
in memory data but its types are for on-disk structure as a result sparse
warns it (different base types).  So fix it by adding new structure
'qgroup_info' to store in memory data and replace on-disk structure
'btrfs_qgroup_info_item' by 'qgroup_info'.  In addition in alloc_cnt()
'generation' is set but not used after that so remove the relevant code.

Signed-off-by: Byongho Lee <bhlee.kernel@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>