sms_route_mt_sms: Don't return uninitialized variable

Wen there's no SMPP support compiled in, and routing was successful,
we shouldn't return an uninitialized value.

Change-Id: I4abbbb5ab336a7e8da08d682f396baec3b56fa3a
Fixes: Coverity CID#174176
diff --git a/src/libmsc/gsm_04_11.c b/src/libmsc/gsm_04_11.c
index 99adbf7..103c259 100644
--- a/src/libmsc/gsm_04_11.c
+++ b/src/libmsc/gsm_04_11.c
@@ -388,7 +388,8 @@
 		rc = GSM411_RP_CAUSE_MO_NUM_UNASSIGNED;
 		rate_ctr_inc(&conn->network->msc_ctrs->ctr[MSC_CTR_SMS_NO_RECEIVER]);
 #endif
-	}
+	} else
+		rc = 0;
 
 	return rc;
 }