Previous patch modified the in memory struct but it's not written in
quota tree until next commit.
So user will still get old data using "btrfs qgroup show" after
assign/remove.

This patch will call btrfs_run_qgroups in assign ioctl so it will be
updated to in memory quota trees and user will get up-to-date results.
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>