UBSAN catches an uninitialized use of the 'preempted' variable in
fork_hap_allocation when there is no preemption.
Fixes: 41548c5472a ("mem_sharing: VM forking") Signed-off-by: Tamas K Lengyel <tamas@tklengyel.com> Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>