KVM: Fix the bitmap range to copy during clear dirty
kvm_dirty_bitmap_bytes() will return the size of the dirty bitmap of
the memslot rather than the size of bitmap passed over from the ioctl.
Here for KVM_CLEAR_DIRTY_LOG we should only copy exactly the size of
bitmap that covers kvm_clear_dirty_log.num_pages.
Signed-off-by: Peter Xu <peterx@redhat.com> Cc: stable@vger.kernel.org Fixes: 2a31b9db153530df4aa02dac8c32837bf5f47019 Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>