fix missing '\' at end of line in Makefile.am

... causing header files to be missing from 'make dist'.

this was introduced in ba874b82be0ad1752b46009ba403f9b7bf24492d
diff --git a/openbsc/include/openbsc/Makefile.am b/openbsc/include/openbsc/Makefile.am
index 7c6bcbe..74e052b 100644
--- a/openbsc/include/openbsc/Makefile.am
+++ b/openbsc/include/openbsc/Makefile.am
@@ -6,7 +6,7 @@
 		 silent_call.h mgcp.h meas_rep.h rest_octets.h \
 		 system_information.h handover.h mgcp_internal.h \
 		 vty.h socket.h e1_config.h trau_upqueue.h token_auth.h \
-		 handover_decision.h rrlp.h
+		 handover_decision.h rrlp.h \
 		crc24.h gprs_llc.h gprs_gmm.h \
 		gb_proxy.h gprs_sgsn.h gsm_04_08_gprs.h sgsn.h \
 		auth.h osmo_msc.h bsc_msc.h bsc_nat.h \