Fix WREDUCE on FF not fixing ARST_VALUE parameter.

Adds test case that fails without code change.

Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>

tests/opt/opt_ff.v

@@ -0,0 +1,21 @@
+module top(
+    input clk,
+    input rst,
+    input [2:0] a,
+    output [1:0] b
+);
+    reg [2:0] b_reg;
+    initial begin
+        b_reg <= 3'b0;
+    end
+
+    assign b = b_reg[1:0];
+    always @(posedge clk or posedge rst) begin
+        if(rst) begin
+            b_reg <= 3'b0;
+        end else begin
+            b_reg <= a;
+        end
+    end
+endmodule
+

tests/opt/opt_ff.ys

@@ -0,0 +1,3 @@
+read_verilog opt_ff.v
+synth_ice40
+ice40_unlut