Update grammar.py to fix parsing errors

[Moneysac90]

I encountered multiple parsing errors because the unit_address is considered being a hex value. This will fail on e.g. the following type of nodes.

node with a hex value but 0x prefixed

uart@0x8000000 {
	compatible = "xlnx";
	reg = <0x1000>;
	interrupts = <0x3b 0x00>;
	clock = <0x2faf080>;
};

node using a variable name some_var instead of an address

uart@some_var {
	compatible = "xlnx";
	reg = <0x1000>;
	interrupts = <0x3b 0x00>;
	clock = <0x2faf080>;
};

node using invalid hex values (in the practice we saw multiple files using float values)

uart@0,0 {
	compatible = "xlnx";
	reg = <0x1000>;
	interrupts = <0x3b 0x00>;
	clock = <0x2faf080>;
};