I was gonna reject this but decided against it. The change is way too simple to justify a rejection, anyway.
The main problem would be that you use CMP instead of AND. While by itself it might not look too bad in a block like this, there are occasions where players leave, say, their Y key pressed while pressing up in the block, and it wouldn't work because of you comparing the exact button press of Up/Down. By using AND (or BIT) players could have other buttons pressed alongside those and the block can still do its intended job.
You also can move the Return: label to the second RTL, removing the last RTL to save a byte.
The code can be even more optimized, using X to hold the sound value while A does the button checks - here's how I'd do it.
Anyways though, good job with it! Feels kinda weird that the volume does not constantly change volume if I hold the arrow, but whatever, and I couldn't figure out how to do that too anyway.