booth: Extend test to catch bug from previous commit

tests/techmap/booth.ys

@@ -1 +1,15 @@
-test_cell -s 1694091355 -n 100 -script booth_map_script.ys_ $mul
+read_verilog <<EOF
+module test(clk, a, b, y);
+	input wire clk;
+	input wire [9:0] a;
+	input wire [6:0] b;
+	output wire [20:0] y;
+
+	assign y = a * b;
+endmodule
+EOF
+booth
+sat -verify -set a 0 -set b 0 -prove y 0
+design -reset
+
+test_cell -s 1694091355 -n 100 -script booth_map_script.ys_ $mul