drm/msm/dpu: Fix uninitialized variable in dpu_crtc_kickoff_clone_mode()

After the loop there is a check for whether "wb_encoder" has been set
to non-NULL, however it was never set to NULL.  Initialize it to NULL.

Fixes: ad06972 ("drm/msm/dpu: Reorder encoder kickoff for CWB")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/641631/
Link: https://lore.kernel.org/r/f8ba03dc-0f90-4781-8d54-c16b3251ecb1@stanley.mountain
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

Author: Dan Carpenter

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

@@ -956,7 +956,7 @@ static int _dpu_crtc_wait_for_frame_done(struct drm_crtc *crtc)
 static int dpu_crtc_kickoff_clone_mode(struct drm_crtc *crtc)
 {
 	struct drm_encoder *encoder;
-	struct drm_encoder *rt_encoder = NULL, *wb_encoder;
+	struct drm_encoder *rt_encoder = NULL, *wb_encoder = NULL;
 	struct dpu_kms *dpu_kms = _dpu_crtc_get_kms(crtc);
 
 	/* Find encoder for real time display */