drm/msm: dpu: Fix "WARNING: invalid free of devm_ allocated data"

'dpu_enc' is a member of 'drm_enc'
And 'drm_enc' got allocated with devm_kzalloc in dpu_encoder_init.

This gives this error message:
./drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:459:1-6:
 WARNING: invalid free of devm_ allocated data
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c

@@ -488,8 +488,6 @@ static void dpu_encoder_destroy(struct drm_encoder *drm_enc)
 
 	drm_encoder_cleanup(drm_enc);
 	mutex_destroy(&dpu_enc->enc_lock);
-
-	kfree(dpu_enc);
 }
 
 void dpu_encoder_helper_split_config(