drm/i915: Fix HPLL watermark readout for g4x

If HPLL watermarks are already enabled, let's not mark them as
disabled by forgetting to bump 'level' before we call
g4x_raw_plane_wm_set().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210514125751.17075-6-ville.syrjala@linux.intel.com


Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>