drm/i915: Remove unused condition in hsw_power_well_post_enable()

We don't use this function on gen9, no need for that test here.

Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>