norflash erase last address calculation error

[CosmicRoach]

embarc_osp/device/peripheral/flash/w25qxx/spi_flash_w25qxx.c

Line 267 in 67ea926

last_address = (address + size) & (~(dev->sector_sz - 1));

Use the size to calculate the last address needs to subtract 1:
last_address = (address + size -1) & (~(dev->sector_sz - 1));

[abrodkin]

@CosmicRoach could you please submit a pull-request with the proposed fix?