char-device: Refactor spice_char_device_client_add a bit
char-device: Refactor spice_char_device_client_add a bit

Factor out CharDeviceClientState creation out of
spice_char_device_client_add.

Acked-by: Frediano Ziglio <55d48b080b2e443e395cde84d2c83b135a4ff48e@redhat.com>

fgouget/spice,SPICE/spice,SPICE/spice,fgouget/spice,fgouget/spice,SPICE/spice,fgouget/spice