Use new stat item/ctr getter APIs

Generated with spatch:
"""
@@
expression E1, E2;
@@
- &E2->ctr[E1]
+ rate_ctr_group_get_ctr(E2, E1)
"""

Change-Id: I2e064883ac6dafa89e41a297a886a9ebd26ce925
diff --git a/src/sgsn/gprs_ranap.c b/src/sgsn/gprs_ranap.c
index e8addd7..ead20f7 100644
--- a/src/sgsn/gprs_ranap.c
+++ b/src/sgsn/gprs_ranap.c
@@ -232,7 +232,7 @@
 
 	mmctx = sgsn_mm_ctx_by_ue_ctx(MSG_IU_UE_CTX(msg));
 	if (mmctx) {
-		rate_ctr_inc(&mmctx->ctrg->ctr[GMM_CTR_PKTS_SIG_IN]);
+		rate_ctr_inc(rate_ctr_group_get_ctr(mmctx->ctrg, GMM_CTR_PKTS_SIG_IN));
 		if (ra_id)
 			memcpy(&mmctx->ra, ra_id, sizeof(mmctx->ra));
 	}