fs/xfs: fix f_ffree value for statfs when project quota is set

When project is set, we should use inode limit minus the used count
Signed-off-by: NYe Yin <dbyin@tencent.com>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_qm_bhv.c

@@ -40,7 +40,7 @@ xfs_fill_statvfs_from_dquot(
 		statp->f_files = limit;
 		statp->f_ffree =
 			(statp->f_files > dqp->q_res_icount) ?
-			 (statp->f_ffree - dqp->q_res_icount) : 0;
+			 (statp->f_files - dqp->q_res_icount) : 0;
 	}
 }