edtlib: silence type checker issue

Mypy is complaining about this line for some reason I didn't have time
to figure out. Just shut it up for now; I'll look into this when I get
around to type annotating edtlib.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

scripts/dts/python-devicetree/src/devicetree/edtlib.py

@@ -79,7 +79,7 @@ try:
     # This makes e.g. gen_defines.py more than twice as fast.
     from yaml import CLoader as Loader
 except ImportError:
-    from yaml import Loader
+    from yaml import Loader     # type: ignore
 
 from devicetree.dtlib import DT, DTError, to_num, to_nums, Type
 from devicetree.grutils import Graph