The string literal has type const char[19]. In the expression it is converted to the pointer to the first its element that is to const char * When this pointer is casted to uint8_t ( (uint8_t) ) though if to use a casting then it would be more correctly to write ( const uint8_t ). So the correct statement should look like
staticconst uint8_t * song = (const uint8_t*)"C2.C2,D4,C4,F4,E8,";