Makefile.am: fix missing LTLDFLAGS for libosmocoding

Despite the libosmocoding.map is preset since the library release,
one was not used in a proper way. The LTLDFLAGS were missing, so
let's add them.

Change-Id: Idf677825ff642d50bea43c7f970810783e864fdd
diff --git a/src/coding/Makefile.am b/src/coding/Makefile.am
index 06e55e5..dcbbd8f 100644
--- a/src/coding/Makefile.am
+++ b/src/coding/Makefile.am
@@ -22,6 +22,7 @@
 	gsm0503_parity.c \
 	gsm0503_coding.c
 libosmocoding_la_LDFLAGS = \
+	$(LTLDFLAGS_OSMOCODING) \
 	-version-info \
 	$(LIBVERSION) \
 	-no-undefined \