quota: Make VFS quotas use new interface for getting quota info

Create new internal interface for getting information about quota which
contains everything needed for both VFS quotas and XFS quotas. Make VFS
use this and hook it up to Q_GETINFO.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e061e66..d348c7d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1076,7 +1076,7 @@
 	.quota_on	= ext4_quota_on,
 	.quota_off	= ext4_quota_off,
 	.quota_sync	= dquot_quota_sync,
-	.get_info	= dquot_get_dqinfo,
+	.get_state	= dquot_get_state,
 	.set_info	= dquot_set_dqinfo,
 	.get_dqblk	= dquot_get_dqblk,
 	.set_dqblk	= dquot_set_dqblk