codec: Add the missing bits for include to install and pkgconfig to work

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/include/osmocom/Makefile.am b/include/osmocom/Makefile.am
index fd9074c..ec548fb 100644
--- a/include/osmocom/Makefile.am
+++ b/include/osmocom/Makefile.am
@@ -1,5 +1,5 @@
 if ENABLE_VTY
-SUBDIRS = vty crypt
+SUBDIRS = vty codec crypt
 else
-SUBDIRS = crypt
+SUBDIRS = codec crypt
 endif