fix instr invld bug

src/verilog/cpu/control_unit.sv

@@ -150,14 +150,18 @@ module control_unit (
     output logic ebreak_o
 );
 
-  logic [6:0] opcode = instr_i[6:0];
-  logic [2:0] funct3 = instr_i[14:12];
-  logic funct7 = instr_i[30];
+  logic [6:0] opcode;
+  logic [2:0] funct3;
+  logic funct7;
   logic [1:0] alu_op;
   logic instr_invld_md;
   logic instr_invld_ad;
   logic branch_o;
 
+  assign opcode   = instr_i[6:0];
+  assign funct3   = instr_i[14:12];
+  assign funct7   = instr_i[30];
+
   assign ebreak_o = (opcode == 7'b1110011) && (funct3 == 3'b000) && (instr_i[31:20] == 12'h1);
 
   main_decoder md (