CVE-2026-72282: KVM: Move kvm_io_bus_get_dev() locking responsibilities to callers

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

KVM: Move kvmiobusgetdev() locking responsibilities to callers

kvmiobusgetdev() returns a device that is only matched by the address, and nothing else. This can cause a lifetime issue if the matched device is not the expected type, as by the time the caller can introspect the object, it might be gone (the srcu lock having been dropped).

Given that there is only a single user of this helper, the simplest option is to move the locking responsibility to the caller, which can keep the srcu lock held for as long as it wants.

Note that this aligns with other kvmiobus() helpers, which already require the srcu lock to be held by the callers.