CVE-2026-43248

In the Linux kernel, the following vulnerability has been resolved:

vhost: move vdpa group bound check to vhost_vdpa

Remove duplication by consolidating these here.  This reduces the
posibility of a parent driver missing them.

While we're at it, fix a bug in vdpa_sim where a valid ASID can be
assigned to a group equal to ngroups, causing an out of bound write.