fix: replace UNUSEDPARAM/UNUSEDSIGNAL with UNUSED for verilator lint

Verilator does not recognize UNUSEDPARAM or UNUSEDSIGNAL.
Correct suppression code is UNUSED.

rtl/ip/mlkem/ntt/barrett_mul.v

@@ -27,9 +27,9 @@ module barrett_mul (
 
     // Compute t_shifted = (p * K) >> 24
     // Use explicit wire for the product to control width
-    /* verilator lint_off UNUSEDSIGNAL */
+    /* verilator lint_off UNUSED */
     wire [36:0] t_product;
-    /* verilator lint_on UNUSEDSIGNAL */
+    /* verilator lint_on UNUSED */
     assign t_product = p_ext * K;
     wire [12:0] t_shifted;
     assign t_shifted = t_product[36:R];