KVM: PPC: Fix kvm_arch_vcpu_ioctl vcpu_load leak

vcpu_put is not called if the user copy fails. This can result in preempt
notifier corruption and crashes, among other issues.

Fixes: b3cebfe8 ("KVM: PPC: Move vcpu_load/vcpu_put down to each ioctl case in kvm_arch_vcpu_ioctl")
Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210716024310.164448-2-npiggin@gmail.com