soundwire: only handle alert events when the peripheral is attached

It doesn't make sense to handle an alert event when the peripheral is
not attached. The slave->status could be SDW_SLAVE_ATTACHED or
SDW_SLAVE_ALERT when it is attached on the bus.

Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>

Author: bardliao

drivers/soundwire/bus.c

@@ -1958,6 +1958,10 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 			break;
 
 		case SDW_SLAVE_ALERT:
+			if (slave->status != SDW_SLAVE_ATTACHED &&
+			    slave->status != SDW_SLAVE_ALERT)
+				continue;
+
 			ret = sdw_handle_slave_alerts(slave);
 			if (ret < 0)
 				dev_err(&slave->dev,