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The declaration was removed earlier, but got accidentally resurrected in
i915xx_wm.[ch] refactoring. Remove harder.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230419115449.422214-1-jani.nikula@intel.com