kvm tools: Rename struct disk_image_operations ops name for raw image

This patch renames:

raw_image__read_sector_ro_mmap to raw_image__read_sector
raw_image__write_sector_ro_mmap to raw_image__write_sector
raw_image__close_ro_mmap to raw_image__close

Signed-off-by: Asias He <asias.hejun@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>