Devicetree: edtlib: fix possible KeyError in Binding.description

Attempting to access the Binding.description property
when the description is unavailable would raise KeyError: 'description'.

Known bindings that won't define a 'description' key in the
Binding.raw dictionary include the 'compatible' property's binding
of nodes such as /, /soc, /leds or /pwmleds.
Note that this may also occur when a proper YAML
binding file is available (e.g. pwmleds.yaml).

This patch simply substitutes the Binding.raw dictionary indexing
with the get() function: will return None and not raise KeyError.

Signed-off-by: Chris Duf <chris@openmarl.org>
diff --git a/scripts/dts/python-devicetree/src/devicetree/edtlib.py b/scripts/dts/python-devicetree/src/devicetree/edtlib.py
index d54075d..7fcbe9c 100644
--- a/scripts/dts/python-devicetree/src/devicetree/edtlib.py
+++ b/scripts/dts/python-devicetree/src/devicetree/edtlib.py
@@ -1695,7 +1695,7 @@
       The absolute path to the file defining the binding.
 
     description:
-      The free-form description of the binding.
+      The free-form description of the binding, or None.
 
     compatible:
       The compatible string the binding matches.
@@ -1829,7 +1829,7 @@
     @property
     def description(self):
         "See the class docstring"
-        return self.raw['description']
+        return self.raw.get('description')
 
     @property
     def compatible(self):