stream_xbar: Use $sformatf() for assert msg

Use $sformatf() to compose a formatted string before passing it as
descriptive message to the assertions macros.

src/stream_xbar.sv

@@ -178,14 +178,14 @@ module stream_xbar #(
 
   if (AxiVldRdy) begin : gen_handshake_assertions
     for (genvar i = 0; unsigned'(i) < NumInp; i++) begin : gen_inp_assertions
-      `ASSERT(input_data_unstable, valid_i[i] && !ready_o[i] |=> $stable(data_i[i] & AxiVldMask), clk_i, !rst_ni, "data_i is unstable at input: %0d", i)
-      `ASSERT(input_sel_unstable, valid_i[i] && !ready_o[i] |=> $stable(sel_i[i]), clk_i, !rst_ni, "sel_i is unstable at input: %0d", i)
-      `ASSERT(input_valid_taken, valid_i[i] && !ready_o[i] |=> valid_i[i], clk_i, !rst_ni, "valid_i at input %0d has been taken away without a ready.", i)
+      `ASSERT(input_data_unstable, valid_i[i] && !ready_o[i] |=> $stable(data_i[i] & AxiVldMask), clk_i, !rst_ni, $sformatf("data_i is unstable at input: %0d", i))
+      `ASSERT(input_sel_unstable, valid_i[i] && !ready_o[i] |=> $stable(sel_i[i]), clk_i, !rst_ni, $sformatf("sel_i is unstable at input: %0d", i))
+      `ASSERT(input_valid_taken, valid_i[i] && !ready_o[i] |=> valid_i[i], clk_i, !rst_ni, $sformatf("valid_i at input %0d has been taken away without a ready.", i))
     end
     for (genvar i = 0; unsigned'(i) < NumOut; i++) begin : gen_out_assertions
-      `ASSERT(output_data_unstable, valid_o[i] && !ready_i[i] |=> $stable(data_o[i] & AxiVldMask), clk_i, !rst_ni, "data_o is unstable at output: %0d Check that parameter LockIn is set.", i)
-      `ASSERT(output_idx_unstable, valid_o[i] && !ready_i[i] |=> $stable(idx_o[i]), clk_i, !rst_ni, "idx_o is unstable at output: %0d Check that parameter LockIn is set.", i)
-      `ASSERT(output_valid_taken, valid_o[i] && !ready_i[i] |=> valid_o[i], clk_i, !rst_ni, "valid_o at output %0d has been taken away without a ready.", i)
+      `ASSERT(output_data_unstable, valid_o[i] && !ready_i[i] |=> $stable(data_o[i] & AxiVldMask), clk_i, !rst_ni, $sformatf("data_o is unstable at output: %0d Check that parameter LockIn is set.", i))
+      `ASSERT(output_idx_unstable, valid_o[i] && !ready_i[i] |=> $stable(idx_o[i]), clk_i, !rst_ni, $sformatf("idx_o is unstable at output: %0d Check that parameter LockIn is set.", i))
+      `ASSERT(output_valid_taken, valid_o[i] && !ready_i[i] |=> valid_o[i], clk_i, !rst_ni, $sformatf("valid_o at output %0d has been taken away without a ready.", i))
     end
   end