qemu_domain: Deduplicate targetNode check in qemuDomainDefValidateMemoryHotplugDevice()

qemu_domain: Deduplicate targetNode check in qemuDomainDefValidateMemoryHotplugDevice()

If a domain has NUMA configured, then all <memory/> devices
(except for 'virtio-pmem') need to have targetNode set. There are
two checks inside of qemuDomainDefValidateMemoryHotplugDevice()
for this: one inside of big switch() statement, which only checks
'dimm' and 'nvdimm' cases, and the other at the end of the
function that checks all models (except for 'virtio-pmem'). Let's
keep the latter and remove the former as the latter covers the
former too.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Kristina Hanicova <khanicov@redhat.com>