drm/i915: WARN if PLL ref/unref got messed up

Spew a WARN if we try to ref/unref the same DPLL multiple
times for the same pipe.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220921211525.10675-5-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>