drm/i915: Remove the PS_PWR_GATE write from skl_program_scaler()

If we don't need the PS_PWR_GATE write when programming the
pipe scaler I don't see why we'd need it for plane scalers either.
Just remove it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181101150605.18235-4-ville.syrjala@linux.intel.com


Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>