drm/i915: Fix workarounds on Gen2-3

In 36537275 ("drm/i915: Simplify internal helper function signature")
I broke the old platforms by not noticing engine workaround init does not
initialize the list on old platforms. Fix it by always initializing which
already does the right thing by mostly not doing anything if there aren't
any workarounds on the list.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: 36537275 ("drm/i915: Simplify internal helper function signature")
Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221118115249.2683946-1-tvrtko.ursulin@linux.intel.com