CODEOWNERS: Adding myself for channeld and spenderp

Adding me as the review for any splicing or channeld related code.

Changelog-None

Author: ddustin

.github/CODEOWNERS

@@ -15,5 +15,8 @@ contrib/pyln-testing/   @cdecker
 # Needed to ensure hsmd wire compatibility between releases
 hsmd/hsmd_wire.csv      @cdecker @ksedgwic @devrandom
 
+channeld/               @ddustin
+plugin/spenderp         @ddustin
+
 # See https://help.github.com/articles/about-codeowners/ for more
 # information