KVM: PPC: fix uninitialized variable warning in kvm_ppc_core_deliver_interrupts

Fixes:
arch/powerpc/kvm/booke.c: In function 'kvmppc_core_deliver_interrupts':
arch/powerpc/kvm/booke.c:147: warning: 'msr_mask' may be used uninitialized in this function

Signed-off-by: Asias He <asias.hejun@gmail.com>
Signed-off-by: Avi Kivity <avi@redhat.com>