drm/komeda: remove set but not used variable 'old'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/arm/display/komeda/komeda_plane.c:
 In function komeda_plane_atomic_duplicate_state:
drivers/gpu/drm/arm/display/komeda/komeda_plane.c:161:35:
 warning: variable old set but not used [-Wunused-but-set-variable

It is not used since commit 990dee3a ("drm/komeda:
Computing image enhancer internally")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190722055627.38008-1-yuehaibing@huawei.com

drivers/gpu/drm/arm/display/komeda/komeda_plane.c

@@ -158,7 +158,7 @@ static void komeda_plane_reset(struct drm_plane *plane)
 static struct drm_plane_state *
 komeda_plane_atomic_duplicate_state(struct drm_plane *plane)
 {
-	struct komeda_plane_state *new, *old;
+	struct komeda_plane_state *new;
 
 	if (WARN_ON(!plane->state))
 		return NULL;
@@ -169,8 +169,6 @@ komeda_plane_atomic_duplicate_state(struct drm_plane *plane)
 
 	__drm_atomic_helper_plane_duplicate_state(plane, &new->base);
 
-	old = to_kplane_st(plane->state);
-
 	return &new->base;
 }