KVM: PPC: Book3S PR: Free shared page if mmu initialization fails

Explicitly free the shared page if kvmppc_mmu_init() fails during
kvmppc_core_vcpu_create(), as the page is freed only in
kvmppc_core_vcpu_free(), which is not reached via kvm_vcpu_uninit().

Fixes: 96bc451a

 ("KVM: PPC: Introduce shared page")
Cc: stable@vger.kernel.org
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Acked-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>