Improve tests to check that clkbuf is connected to expected
Improve tests to check that clkbuf is connected to expected

SymbiFlow/yosys,YosysHQ/yosys,YosysHQ/yosys,cliffordwolf/yosys,cliffordwolf/yosys,YosysHQ/yosys,antmicro/yosys,cliffordwolf/yosys,antmicro/yosys,SymbiFlow/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,antmicro/yosys,antmicro/yosys,SymbiFlow/yosys,SymbiFlow/yosys,YosysHQ/yosys,cliffordwolf/yosys,cliffordwolf/yosys,cliffordwolf/yosys,antmicro/yosys,cliffordwolf/yosys,cliffordwolf/yosys,cliffordwolf/yosys,SymbiFlow/yosys,antmicro/yosys,SymbiFlow/yosys,SymbiFlow/yosys,antmicro/yosys,antmicro/yosys,SymbiFlow/yosys