fix unused param

PiperOrigin-RevId: 350389614
diff --git a/hwy/ops/scalar-inl.h b/hwy/ops/scalar-inl.h
index e878192..f5cc359 100644
--- a/hwy/ops/scalar-inl.h
+++ b/hwy/ops/scalar-inl.h
@@ -861,7 +861,7 @@
 }
 
 template <typename T>
-HWY_API Vec1<T> Compress(Vec1<T> v, const Mask1<T> mask) {
+HWY_API Vec1<T> Compress(Vec1<T> v, const Mask1<T> /* mask */) {
   // Upper lanes are undefined, so result is the same independent of mask.
   return v;
 }