drm/xe: correct the calculation of remaining size

In function write_pgtable, the calculation of chunk in the do-while
loop is wrong, we should always compare against remaining size instead
of the total size update->qwords.

Signed-off-by: Fei Yang <fei.yang@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240116223709.652585-2-fei.yang@intel.com