drm/i915: Remove redundant check for DG1

dg1_gt_workarounds_init() is only ever called for DG1, so there is no
point checking it again.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230306204954.753739-1-lucas.demarchi@intel.com