build: distcheck: add missing distclean files

Change-Id: I24d72b2b1bae52a1b2cf8a989396d2aac31d119e
diff --git a/include/osmocom/ranap/Makefile.am b/include/osmocom/ranap/Makefile.am
index 4728ac8..0f83e03 100644
--- a/include/osmocom/ranap/Makefile.am
+++ b/include/osmocom/ranap/Makefile.am
@@ -593,3 +593,6 @@
 	RANAP_VoiceSupportMatchIndicator.h
 
 ranapdir = $(includedir)/osmocom/ranap
+
+DISTCLEANFILES = \
+	ranap_ies_defs.h