Btrfs: fix confusing edquot happening case
Btrfs: fix confusing edquot happening case

Step to reproduce:
	mkfs.btrfs <disk>
	mount <disk> <mnt>
	dd if=/dev/zero of=/<mnt>/data bs=1M count=10
	sync
	btrfs quota enable <mnt>
	btrfs qgroup create 0/5 <mnt>
	btrfs qgroup limit 5M 0/5 <mnt>
	rm -f /<mnt>/data
	sync
	btrfs qgroup show <mnt>
	dd if=/dev/zero of=data bs=1M count=1

>From the perspective of users, qgroup's referenced or exclusive
is negative,but user can not continue to write data! a workaround
way is to cast u64 to s64 when doing qgroup reservation.

Signed-off-by: Wang Shilong <2619f00d4b1c70e3aae124ec60dac0e454c5a3a3@cn.fujitsu.com>
Reviewed-by: Arne Jansen <1ac75ecdee0e8d99a7251fd3af35e29d91a85db3@gmx.net>
Signed-off-by: Josef Bacik <631dfb3d07694fdcf26abc7aac2c6c2b641f8bde@fusionio.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs