intel: ssp: drain RX fifo when starting

If DMA transaction is ongoing when RX is enabled, this can lead
to stuck communication between DMA and SSP (DMA service request
not seen by the DMA).

To avoid this, flush the RX fifo before enabling SSP RX.

Link: https://github.com/thesofproject/sof/issues/7548
Suggested-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>

src/drivers/intel/ssp/ssp.c

@@ -975,6 +975,10 @@ static void ssp_early_start(struct dai *dai, int direction)
 
 	key = k_spin_lock(&dai->lock);
 
+	/* RX fifo must be cleared before start */
+	if (direction == DAI_DIR_CAPTURE)
+		ssp_empty_rx_fifo(dai);
+
 	/* request mclk/bclk */
 	ssp_pre_start(dai);