Fix off by one in spi dump
Fix off by one in spi dump

Need to increment by 256 rather than 255 to make the address of the next
block the address after the end of the current one. This fixes a bug
where the last byte of a block is always repeated as the first byte of
the next.

greatscottgadgets/greatfet,dominicgs/GreatFET-experimental,greatscottgadgets/greatfet,dominicgs/GreatFET-experimental,greatscottgadgets/greatfet,greatscottgadgets/greatfet,dominicgs/GreatFET-experimental