drm/i915: Remove the repeated declaration

Function 'intel_dbuf_init' is declared twice, remove the
repeated declaration.

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1621927793-44545-1-git-send-email-zhangshaokun@hisilicon.com

drivers/gpu/drm/i915/intel_pm.h

@@ -83,8 +83,6 @@ struct intel_dbuf_state {
 	bool joined_mbus;
 };
 
-int intel_dbuf_init(struct drm_i915_private *dev_priv);
-
 struct intel_dbuf_state *
 intel_atomic_get_dbuf_state(struct intel_atomic_state *state);