kvm: selftests: aarch64: dirty_log_test: fix unaligned memslot size

The memory slot size must be aligned to the host's page size. When
testing a guest with a 4k page size on a host with a 64k page size,
then 3 guest pages are not host page size aligned. Since we just need
a nearly arbitrary number of extra pages to ensure the memslot is not
aligned to a 64 host-page boundary for this test, then we can use
16, as that's 64k aligned, but not 64 * 64k aligned.

Fixes: 76d58e0f

 ("KVM: fix KVM_CLEAR_DIRTY_LOG for memory slots of unaligned size", 2019-04-17)
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>