ovsdb-client: Use correct operand to 'sizeof' in do_dump().

ovsdb-client: Use correct operand to 'sizeof' in do_dump().

When copying an object, one must calculate the size of the object itself,
not of its address.

No visible effect, though, since both the object and its address are
pointers in this case.

Found by Coverity.

Reported-at: https://scan3.coverity.com/reports.htm#v16889/p10449/fileInstanceId=14762869&defectInstanceId=4304032&mergedDefectId=179550
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Aaron Conole <aconole@redhat.com>