osmo_get_rand_id(): Avoid dead code by proper #if/#else/#endif

Change-Id: I34e465dead179487f7d4508e0e6ecf0e838c6eb7
Closes: CID#177910
diff --git a/src/gsm/gsm_utils.c b/src/gsm/gsm_utils.c
index f154c2b..365920f 100644
--- a/src/gsm/gsm_utils.c
+++ b/src/gsm/gsm_utils.c
@@ -466,8 +466,9 @@
 	if (rc < 0) {
 #if (USE_GNUTLS)
 		return gnutls_rnd(GNUTLS_RND_RANDOM, out, len);
-#endif
+#else
 		return -errno;
+#endif
 	}
 
 	/* getrandom() failed partially due to signal interruption: