Stop GTFS component from overwriting friendly_name (#3798)

* Prevent update from clobbering configured name.

* linted

* Fixing awkward line breaking.

homeassistant/components/sensor/gtfs.py

@@ -185,7 +185,8 @@ class GTFSDepartureSensor(Entity):
         self._pygtfs = pygtfs
         self.origin = origin
         self.destination = destination
-        self._name = name
+        self._custom_name = name
+        self._name = ''
         self._unit_of_measurement = 'min'
         self._state = 0
         self._attributes = {}
@@ -233,9 +234,10 @@ class GTFSDepartureSensor(Entity):
             trip = self._departure['trip']
 
             name = '{} {} to {} next departure'
-            self._name = name.format(agency.agency_name,
-                                     origin_station.stop_id,
-                                     destination_station.stop_id)
+            self._name = (self._custom_name or
+                          name.format(agency.agency_name,
+                                      origin_station.stop_id,
+                                      destination_station.stop_id))
 
             # Build attributes
             self._attributes = {}