kvm-all: PAGE_SIZE should be real host page size

Just noticed this while grepping TARGET_PAGE_SIZE for an unrelated
reason. I didn't use qemu_real_host_page_size as kvm_set_phys_mem()
does, because we'd need to make sure page_size_init() has run first.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Message-Id: <1447115022-4142-1-git-send-email-drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>