fix(mlkem): verilator lint fixes — BLKLOOPINIT and UNUSEDSIGNAL

ntt_core.v / poly_mul_sync.v: <= → = in array for loops
mlkem_top.v / sha3_top.v: UNUSEDSIGNAL → UNUSED

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

rtl/ip/mlkem/ntt/ntt_core.v

@@ -147,7 +147,7 @@ module ntt_core (
             valid_o_r <= 1'b0;
             scale_valid_i <= 1'b0;
             scale_a_i <= 12'd0;
-            for (ci = 0; ci < N; ci = ci + 1) cr[ci] <= 12'd0;
+            for (ci = 0; ci < N; ci = ci + 1) cr[ci] = 12'd0;
         end else begin
             state <= next_state;
             scale_valid_i <= 1'b0;