Wrong, Mohandas Karamchand fought for upper caste Hindus (how many Dalits think MK fought for them, please stand up)
The constitution of India gives Dalits all the rights and more (compared to the "non-dalits"). That would not have been possible in British India. It really does not mater how many Dalits agree, but effectively by fighting for independence Gandhi was fighting for all Indians (incl. Dalits).