osmo_bsc_grace.h: use '<>' include, not '""'

Change-Id: I2f22be93d1a5fd6f229b85305a1d2a2cf6a43ce2
diff --git a/openbsc/include/openbsc/osmo_bsc_grace.h b/openbsc/include/openbsc/osmo_bsc_grace.h
index e9c1a0a..af77b2f 100644
--- a/openbsc/include/openbsc/osmo_bsc_grace.h
+++ b/openbsc/include/openbsc/osmo_bsc_grace.h
@@ -21,7 +21,7 @@
 #ifndef OSMO_BSC_GRACE_H
 #define OSMO_BSC_GRACE_H
 
-#include "gsm_data.h"
+#include <openbsc/gsm_data.h>
 
 struct osmo_msc_data;