SECTOR_SIZE macros since there is a conflicting definition in
`/usr/src/linux-headers-4.19.0-16-common/include/linux/blkdev.h`.
The definitions are nearly identical and that in host/vhost/mic_blk.c could
probably be removed instead of prefixed. I'm just being conservative since I'm
making a bunch of changes at once without the ability to build and test along
the way.