Reduce hunterdouglas_powerview parallel updates (#36299)

The powerview hub gets overwhelmed with just a
few requests so we now set PARALLEL_UPDATES to
1.

homeassistant/components/hunterdouglas_powerview/__init__.py

@@ -56,6 +56,9 @@ from .const import (
     USER_DATA,
 )
 
+PARALLEL_UPDATES = 1
+
+
 DEVICE_SCHEMA = vol.Schema(
     {DOMAIN: vol.Schema({vol.Required(CONF_HOST): cv.string})}, extra=vol.ALLOW_EXTRA
 )

homeassistant/components/hunterdouglas_powerview/cover.py

@@ -45,6 +45,8 @@ _LOGGER = logging.getLogger(__name__)
 # from one state to another
 TRANSITION_COMPLETE_DURATION = 30
 
+PARALLEL_UPDATES = 1
+
 
 async def async_setup_entry(hass, entry, async_add_entities):
     """Set up the hunter douglas shades."""