drm/msm: dpu: Don't reset dpu_enc->cur_master on .disable()

cur_master in dpu_encoder is assigned at modeset and cleared on
.disable(). Unfortunately dpms (or enable/disable) does not guarantee a
modeset, so cur_master is NULL when we try to re-enable it.

This patch moves the NULL assignment to setup_display where it will be
re-assigned later in the function.
Tested-by: Bruce Wang <bzwang@chromium.org>
Reviewed-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>

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

@@ -1230,8 +1230,6 @@ static void dpu_encoder_virt_disable(struct drm_encoder *drm_enc)
 			dpu_enc->phys_encs[i]->connector = NULL;
 	}
 
-	dpu_enc->cur_master = NULL;
-
 	DPU_DEBUG_ENC(dpu_enc, "encoder disabled\n");
 
 	dpu_rm_release(&dpu_kms->rm, drm_enc);
@@ -2073,6 +2071,8 @@ static int dpu_encoder_setup_display(struct dpu_encoder_virt *dpu_enc,
 		return -EINVAL;
 	}
 
+	dpu_enc->cur_master = NULL;
+
 	memset(&phys_params, 0, sizeof(phys_params));
 	phys_params.dpu_kms = dpu_kms;
 	phys_params.parent = &dpu_enc->base;