disp: msm: sde: avoid false error for encoder restore

Below sequence can trigger encoder restore failure due
to cur_master unavailability.
 -> Primary encoder is attached to crtc-0
 -> Primary encoder enters in power collapse state
 -> CWB encoder attached to crtc-0
 -> Atomic_check updates the crtc encoder_mask with
    two encoders.
 -> Prepare_commit triggers power restore
 -> crtc triggers encoder_restore based on encoder_mask

CWB encoder is not enabled at this stage and it will fail
to restore. This patch avoids the error message in this
valid condition.

msm/sde/sde_encoder.c

@@ -3124,7 +3124,7 @@ void sde_encoder_virt_restore(struct drm_encoder *drm_enc)
 	sde_enc = to_sde_encoder_virt(drm_enc);
 
 	if (!sde_enc->cur_master) {
-		SDE_ERROR("virt encoder has no master\n");
+		SDE_DEBUG("virt encoder has no master\n");
 		return;
 	}