Prevent:

-chardev socket,path=/tmp/foo,server,nowait,id=c0 \
-device virtserialport,chardev=c0,id=vs0 \
-device virtserialport,chardev=c0,id=vs1
Reported-by: NMike Cao <bcao@redhat.com>
Signed-off-by: NAmit Shah <amit.shah@redhat.com>