The qed_bytes_to_clusters() function is normally used with size_t
lengths.  Consistency check used it with file size length and therefore
failed on 32-bit hosts when the image file is 4 GB or more.

Make qed_bytes_to_clusters() explicitly 64-bit and update consistency
check to keep 64-bit cluster counts.
Reported-by: NMichael Tokarev <mjt@tls.msk.ru>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>