xfs: remove redundant variable assignment in xfs_symlink()

The variables 'udqp' and 'gdqp' have been initialized, so remove
redundant variable assignment in xfs_symlink().

Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>