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_gb.c b/src/sgsn/gprs_gb.c
index cddd1b1..96157a0 100644
--- a/src/sgsn/gprs_gb.c
+++ b/src/sgsn/gprs_gb.c
@@ -57,7 +57,7 @@
 	bssgp_parse_cell_id(&ra_id, msgb_bcid(msg));
 	mmctx = sgsn_mm_ctx_by_tlli(msgb_tlli(msg), &ra_id);
 	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));
 		mmctx->gb.llme = llme;
 		gprs_gb_recv_pdu(mmctx, msg);
 	}
@@ -102,7 +102,7 @@
 	pinfo.drx_params = mmctx->drx_parms;
 	pinfo.qos[0] = 0; // FIXME
 	rc = bssgp_tx_paging(mmctx->gb.nsei, 0, &pinfo);
-	rate_ctr_inc(&mmctx->ctrg->ctr[GMM_CTR_PAGING_PS]);
+	rate_ctr_inc(rate_ctr_group_get_ctr(mmctx->ctrg, GMM_CTR_PAGING_PS));
 
 	return rc;
 }