KVM: s390: Replace incorrect atomic_or with atomic_andnot

KVM: s390: Replace incorrect atomic_or with atomic_andnot

The offending commit accidentally replaces an atomic_clear with an
atomic_or instead of an atomic_andnot in kvm_s390_vcpu_request_handled.
The symptom is that kvm guests on s390 hang on startup.
This patch simply replaces the incorrect atomic_or with atomic_andnot

Fixes: 805de8f43c20 (atomic: Replace atomic_{set,clear}_mask() usage)
Signed-off-by: Jason J. Herne <[email protected]>
Acked-by: Christian Borntraeger <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Cornelia Huck <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>