mkfs.minix: check requested blocks will not exceed available on device

mkfs.minix: check requested blocks will not exceed available on device

Earlier user could define more blocks than device, or backing file for
loopback file system, had available.  That lead to a system crash with
following commands;

fallocate --length 64KiB test-file
mkfs.minix -3 -i 842160 test-file 104882174
mkdir test-file.d
mount test-file test-file.d
cp /etc/service test-file.d
Killed
sudo umount test-file.d

The minix driver should probably not hang the whole kernel, but the least
that mkfs.minix ought to do is not to let users to get that condition
quite as easily.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>