xfs: remove unnecessary variable udqp from xfs_ioctl_setattr

The initial value of variable udqp is NULL, and we only set the
flag XFS_QMOPT_PQUOTA in xfs_qm_vop_dqalloc() function, so only
the pdqp value is initialized and the udqp value is still NULL.
Since the udqp value is NULL in the rest part of xfs_ioctl_setattr()
function, it is meaningless and do nothing. So remove it from
xfs_ioctl_setattr().

Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>