KVM: add missing compat KVM_CLEAR_DIRTY_LOG

The arguments to the KVM_CLEAR_DIRTY_LOG ioctl include a pointer,
therefore it needs a compat ioctl implementation.  Otherwise,
32-bit userspace fails to invoke it on 64-bit kernels; for x86
it might work fine by chance if the padding is zero, but not
on big-endian architectures.

Reported-by: Thomas Sattler
Cc: stable@vger.kernel.org
Fixes: 2a31b9db

 ("kvm: introduce manual dirty log reprotect")
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>