drm/xe: fix multicast support for Xe_LP platforms

Xe_LP has six sublices per slice.

v2: fixed commit message and subject (Matt)

Bspec: 66696
Fixes: bde5d767

 ("drm/xe: Add helper macro to loop each DSS")
Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240405-mcr_adlp-v2-1-2fd1e4325ef2@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>