Two problems with your code:
1) First, you should have a GPIO peripheral enabled and a specific pin configured as analog input pin.
2) In this function call ADCSequenceStepConfigure(ADC0_BASE, 3, 0, ADC_CTL_TS | ADC_CTL_IE | ADC_CTL_END);
the pin selected for conversion is still the internal temperature sensor (ADC_CTL_TS) - replace it with your analog pin declared above. Also, you don't need to declare ADC_CTL_IE if you do not use ADC interrupts.