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: #7548
Suggested-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
(cherry picked from commit 4a4d8d2)

Author: kv2019i

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);