fsck.cramfs: print correct error on 32-bit systems

fsck.cramfs: print correct error on 32-bit systems

On 32-bit systems the file length check does not handle files correctly
which are larger than 4 GB. Use an unsigned long long which is already
in place for blkdev_get_size.

Proof of Concept:

- Prepare a file containing a CramFS
```
mkdir owo
mkfs.cramfs owo owo.iso
dd if=/dev/zero of=owo.iso bs=1 seek=4294967296 count=1 conv=notrunc
fsck.cramfs owo.iso
```

- Check the file
```
fsck.cramfs owo.iso
```

You will see: `fsck.cramfs: file length too short`
Better message is: `fsck.cramfs: file extends past end of filesystem`

Signed-off-by: Samanta Navarro <ferivoz@riseup.net>