drivers: i2s: stm32_sai fix drain and stop of tx stream

Fix two issues with the SAI TX Stream.

1. Drain command does not release the last memory buffer
2. TX Stream status does not change to READY after STOPPING

Signed-off-by: Mario Paja <mariopaja@hotmail.com>

Author: mariopaja

drivers/i2s/i2s_stm32_sai.c

@@ -134,7 +134,6 @@ void HAL_SAI_TxCpltCallback(SAI_HandleTypeDef *hsai)
 	struct i2s_stm32_sai_data *dev_data = CONTAINER_OF(hsai, struct i2s_stm32_sai_data, hsai);
 	struct stream *stream = &dev_data->stream;
 	struct queue_item item;
-	void *mem_block_tmp;
 	int ret;
 
 	if (stream->state == I2S_STATE_ERROR) {
@@ -154,6 +153,7 @@ void HAL_SAI_TxCpltCallback(SAI_HandleTypeDef *hsai)
 
 	if (stream->last_block) {
 		LOG_DBG("TX Stopped ...");
+		stream->state = I2S_STATE_READY;
 		goto exit;
 	}
 
@@ -171,8 +171,6 @@ void HAL_SAI_TxCpltCallback(SAI_HandleTypeDef *hsai)
 		goto exit;
 	}
 
-	mem_block_tmp = stream->mem_block;
-
 	stream->mem_block = item.buffer;
 	stream->mem_block_len = item.size;
 
@@ -183,9 +181,9 @@ void HAL_SAI_TxCpltCallback(SAI_HandleTypeDef *hsai)
 		LOG_ERR("HAL_SAI_Transmit_DMA: <FAILED>");
 	}
 
-	k_mem_slab_free(stream->i2s_cfg.mem_slab, mem_block_tmp);
 exit:
-	/* EXIT */
+	/* Free memory slab & exit */
+	k_mem_slab_free(stream->i2s_cfg.mem_slab, stream->mem_block);
 }
 
 void HAL_SAI_ErrorCallback(SAI_HandleTypeDef *hsai)