pc: Improve error message when die-id is omitted

pc: Improve error message when die-id is omitted

The error message when die-id is omitted doesn't make sense:

  $ qemu-system-x86_64 -smp 1,sockets=6,maxcpus=6 \
    -device qemu64-x86_64-cpu,socket-id=1,core-id=0,thread-id=0
  qemu-system-x86_64: -device qemu64-x86_64-cpu,socket-id=1,core-id=0,thread-id=0: \
    Invalid CPU die-id: 4294967295 must be in range 0:0

Fix it, so it will now read:

  qemu-system-x86_64: -device qemu64-x86_64-cpu,socket-id=1,core-id=0,thread-id=0: \
    CPU die-id is not set

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20190815183803.13346-3-ehabkost@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Vanderson M. do Rosario <vandersonmr2@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>