soundwire: stream: fix bad unlock balance

the msg lock is taken for multi-link cases only but released
unconditionally, leading to an unlock balance warning for single-link usages
This patch fixes this.

 =====================================
 WARNING: bad unlock balance detected!
 5.1.0-16506-gc1c383a6f0a2-dirty #1523 Tainted: G        W
 -------------------------------------
 aplay/2954 is trying to release lock (&bus->msg_lock) at:
 do_bank_switch+0x21c/0x480
 but there are no more locks to release!

Signed-off-by: Srinivas Kandagatla <[email protected]>
Acked-by: Pierre-Louis Bossart <[email protected]>
Acked-by: Sanyog Kale <[email protected]>
[vkoul: edited the change log as suggested by Pierre]
Signed-off-by: Vinod Koul <[email protected]>

Author: Srinivas-Kandagatla

drivers/soundwire/stream.c

@@ -814,7 +814,8 @@ static int do_bank_switch(struct sdw_stream_runtime *stream)
 			goto error;
 		}
 
-		mutex_unlock(&bus->msg_lock);
+		if (bus->multi_link)
+			mutex_unlock(&bus->msg_lock);
 	}
 
 	return ret;