fix to read sub mA values

[savejeff]

There is an accidental rounding in the getCurrent function.

to fix this you can use this code to get values between full mA

float Sensor_INA3221_Class::getCurrent(ina3221_ch_t channel) {
	int32_t shunt_uV = 0;
	float current_A = 0;

	shunt_uV = getShuntVoltage(channel);
	current_A = ((float) shunt_uV) / ((int32_t)_shuntRes[channel]) / 1000.0f; // <- here previously the value was rounded needlessly
	return current_A;
}