btrfs: qgroup: fix limit args override whole limit struct
btrfs: qgroup: fix limit args override whole limit struct

btrfs_limit_group use arg limit to override the old qgroup_limit of
corresponding qgroup. However, we should override part of old qgroup_limit
according to the bit which has been set in arg limit.

Signed-off-by: Fan Chengniang <801b6f4936a3eeaa6cb40a31ddecb051b8eac9a8@cn.fujitsu.com>
Signed-off-by: Dongsheng Yang <1b957dfff8d0f16ed124fab3c79d8c1232c34692@cn.fujitsu.com>
Signed-off-by: Chris Mason <e2e8c5702d8ed5f565988a1cf5bb35c9ce199e5e@fb.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs