drm/i915: Don't preserve dpll_hw_state for slave crtc in Bigjoiner

drm/i915: Don't preserve dpll_hw_state for slave crtc in Bigjoiner

If we are using Bigjoiner dpll_hw_state is supposed to be exactly
same as for master crtc, so no need to save it's state for slave crtc.

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Fixes: 0ff0e219d9b8 ("drm/i915: Compute clocks earlier")
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230628141017.18937-1-stanislav.lisovskiy@intel.com
(cherry picked from commit cbaf758809952c95ec00e796695049babb08bb60)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>