cosmetic: tweak rc type of is_cm_service_for_emerg()

Change-Id: Id752d3882645708b5b8e1058b6799d3d285286c4
diff --git a/src/osmo-bsc/gsm_08_08.c b/src/osmo-bsc/gsm_08_08.c
index 7789d49..0765d1d 100644
--- a/src/osmo-bsc/gsm_08_08.c
+++ b/src/osmo-bsc/gsm_08_08.c
@@ -105,7 +105,7 @@
 	return 0;
 }
 
-static int is_cm_service_for_emerg(struct msgb *msg)
+static bool is_cm_service_for_emerg(struct msgb *msg)
 {
 	struct gsm48_service_request *cm;
 	struct gsm48_hdr *gh = msgb_l3(msg);