build: distcheck: add missing distclean files

Change-Id: I24d72b2b1bae52a1b2cf8a989396d2aac31d119e
diff --git a/include/osmocom/hnbap/Makefile.am b/include/osmocom/hnbap/Makefile.am
index 83654cb..cd9b720 100644
--- a/include/osmocom/hnbap/Makefile.am
+++ b/include/osmocom/hnbap/Makefile.am
@@ -115,3 +115,6 @@
 	U-RNTIQueryRequest.h \
 	U-RNTIQueryResponse.h \
 	UTRANCellID.h
+
+DISTCLEANFILES = \
+	hnbap_ies_defs.h