btrfs: Report error on removing qgroup if del_qgroup_item fails

btrfs: Report error on removing qgroup if del_qgroup_item fails

Previously, we were calling del_qgroup_item, and ignoring the return code
resulting in a potential to have divergent in-memory state without an
error. Perhaps, it makes sense to handle this error code, and put the
filesystem into a read only, or similar state.

This patch only adds reporting of the error if the error is fatal,
(any error other than qgroup not found).

Signed-off-by: Sargun Dhillon <[email protected]>
Reviewed-by: Qu Wenruo <[email protected]>
Signed-off-by: David Sterba <[email protected]>