KVM: s390: Fix possible memory leak of in kvm_arch_vcpu_create()

This patch fixed possible memory leak in kvm_arch_vcpu_create()
under s390, which would happen when kvm_arch_vcpu_create() fails.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Acked-by: Carsten Otte <cotte@de.ibm.com>
Cc: stable@kernel.org
Signed-off-by: Avi Kivity <avi@redhat.com>