Ensure display-name does not exceed 12 characters for CecAdapter. (#9268)

* Ensure display-name does not exceed 12 characters for CecAdapter.

* Miscalculated offset.

homeassistant/components/hdmi_cec.py

@@ -31,7 +31,7 @@ DOMAIN = 'hdmi_cec'
 
 _LOGGER = logging.getLogger(__name__)
 
-DEFAULT_DISPLAY_NAME = "HomeAssistant"
+DEFAULT_DISPLAY_NAME = "HA"
 CONF_TYPES = 'types'
 
 ICON_UNKNOWN = 'mdi:help'
@@ -181,7 +181,7 @@ def setup(hass: HomeAssistant, base_config):
     if host:
         adapter = TcpAdapter(host, name=display_name, activate_source=False)
     else:
-        adapter = CecAdapter(name=display_name, activate_source=False)
+        adapter = CecAdapter(name=display_name[:12], activate_source=False)
     hdmi_network = HDMINetwork(adapter, loop=loop)
 
     def _volume(call):