Fix ivshmem build on 32-bit hosts

stat() fields can be more or less anything depending on configuration, cast
explicitly to uint64_t to avoid printf() format mismatches.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
(cherry picked from commit ad0a4ac1)