Current usage of kvm_io_device requires users to destruct it with an extra
call of kvm_iodevice_destructor after the device gets unregistered from
kvm_io_bus. This is not necessary and can cause errors if a user forgot
to make the extra call.

Simplify the usage by combining kvm_iodevice_destructor into
kvm_io_bus_unregister_dev. This reduces LOCs a bit for users and can
avoid the leakage of destructing the device explicitly.
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20230207123713.3905-2-wei.w.wang@intel.comSigned-off-by: Sean Christopherson <seanjc@google.com>