build: distcheck: add missing distclean files

Change-Id: I24d72b2b1bae52a1b2cf8a989396d2aac31d119e
diff --git a/src/Makefile.am b/src/Makefile.am
index ffdfef8..3e309db 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -83,3 +83,14 @@
 	$(MAKE) -C hnbap regen
 	$(MAKE) -C ranap regen
 	$(MAKE) -C rua regen
+
+DISTCLEANFILES = \
+	hnbap_decoder.c \
+	hnbap_encoder.c \
+	rua_decoder.c \
+	rua_encoder.c \
+	ranap_decoder.c \
+	ranap_encoder.c \
+	gen_hnbap.stamp \
+	gen_rua.stamp \
+	gen_ranap.stamp