qemu: qemuBuildChardevCommand: use chrSourcePriv unconditionally
qemu: qemuBuildChardevCommand: use chrSourcePriv unconditionally

In the QEMU driver, we allocate private source data unconditionally
for every chardev and the rest of the function just assumes it's there.

Signed-off-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>
Reviewed-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>

crobinso/libvirt,zippy2/libvirt,crobinso/libvirt,jfehlig/libvirt,libvirt/libvirt,olafhering/libvirt,libvirt/libvirt,crobinso/libvirt,olafhering/libvirt,zippy2/libvirt,jfehlig/libvirt,jfehlig/libvirt,jfehlig/libvirt,libvirt/libvirt,olafhering/libvirt,zippy2/libvirt,crobinso/libvirt,olafhering/libvirt,libvirt/libvirt,zippy2/libvirt