drm/i915/display: Squelch kerneldoc warnings

Just a parameter rename,

drivers/gpu/drm/i915/display/intel_display.c:14425: warning: Function parameter or member '_new_plane_state' not described in 'intel_prepare_plane_fb'
drivers/gpu/drm/i915/display/intel_display.c:14425: warning: Excess function parameter 'new_state' description in 'intel_prepare_plane_fb'
drivers/gpu/drm/i915/display/intel_display.c:14534: warning: Function parameter or member '_old_plane_state' not described in 'intel_cleanup_plane_fb'
drivers/gpu/drm/i915/display/intel_display.c:14534: warning: Excess function parameter 'old_state' description in 'intel_cleanup_plane_fb'

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191012080208.18774-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/display/intel_display.c

@@ -14410,7 +14410,7 @@ static void fb_obj_bump_render_priority(struct drm_i915_gem_object *obj)
 /**
  * intel_prepare_plane_fb - Prepare fb for usage on plane
  * @plane: drm plane to prepare for
- * @new_state: the plane state being prepared
+ * @_new_plane_state: the plane state being prepared
  *
  * Prepares a framebuffer for usage on a display plane.  Generally this
  * involves pinning the underlying object and updating the frontbuffer tracking
@@ -14524,7 +14524,7 @@ intel_prepare_plane_fb(struct drm_plane *plane,
 /**
  * intel_cleanup_plane_fb - Cleans up an fb after plane use
  * @plane: drm plane to clean up for
- * @old_state: the state from the previous modeset
+ * @_old_plane_state: the state from the previous modeset
  *
  * Cleans up a framebuffer that has just been removed from a plane.
  */