Small cleanup and fix from Fujitsu

Hi Chris,

This is the small cleanup and fixes for 4.2. Compared to the previous pull, this one is quite small, only 2 cleanup and one small quota fix.

Yang Dongsheng (1):
btrfs: qgroup: allow user to clear the limitation on qgroup

Zhao Lei (2):
btrfs: cleanup noused initialization of dev in btrfs_end_bio()
btrfs: add error handling for scrub_workers_get()

Please pull these small fixes from my tree
https://github.com/adam900710/linux.git for_chris_4.2_part2

Thanks,
Qu