liblzma: mt dec: Fix a comment

Reviewed-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Thanks-to: Sam James <sam@gentoo.org>
(cherry picked from commit 831b55b971cf579ee16a854f177c36b20d3c6999)

src/liblzma/common/stream_decoder_mt.c

@@ -347,7 +347,7 @@ worker_enable_partial_update(void *thr_ptr)
 
 
 /// Things do to at THR_STOP or when finishing a Block.
-/// This is called with thr->mutex locked.
+/// This is called with thr->coder->mutex locked.
 static void
 worker_stop(struct worker_thread *thr)
 {