public Varnode findVarnode(int sz, Address addr, Address pc) {
		return vbank.find(sz, addr, pc, -1);
	}
return first instance of a Varnode with given size, starting Address,
and bound to an instruction at the given Address
@param sz  -- size of Varnode
@param addr -- starting Address of Varnode
@param pc -- Address of instruction writing to Varnode
@return -- the Varnode
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/model/pcode/PcodeSyntaxTree.java