mkfs.minix: add sectorsize check

mkfs.minix: add sectorsize check

Minix filesystem until version 2 has a fixed blocksize of 1024 bytes.
If you try to create a filsystem on a device with a physical sectorsize
larger than 1024 bytes, this resulting minix fs cannot be mounted,
because the physical sectorsize must be smaller than the filesystem
blocksize.
This patch adds a check for this and will refuse to create a filesystem
if the sectorsize is bigger than the blocksize.

Signed-off-by: Matthias Koenig <mkoenig@suse.de>