fix off-by-one generating vmdk backing files (Avi Kivity)

Signed-off-by: Avi Kivity <avi@redhat.com> 
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5567 c046a42c-6fe2-441c-8c8c-71466251a162
