Do not use default values during setup registers by default

[brainelectronics]

As found by #10 the setup_registers function's parameter use_default_vals is set to True by default, leading to unwanted behaviour of using the default values if not explicitly disabled.
see

micropython-modbus/umodbus/modbus.py

Lines 613 to 615 in dd5b8e5

	def setup_registers(self,
	registers: dict = dict(),
	use_default_vals: bool = True) -> None: