pdch is_enabled: Use API getter instead of accessing field directly

Change-Id: I389f42ef2e95d28643ec51771e46d083d4e20057
diff --git a/src/gprs_bssgp_pcu.c b/src/gprs_bssgp_pcu.c
index bf82fc4..8fd6d85 100644
--- a/src/gprs_bssgp_pcu.c
+++ b/src/gprs_bssgp_pcu.c
@@ -782,7 +782,7 @@
 		for (ts_no = 0; ts_no < ARRAY_SIZE(trx->pdch); ++ts_no) {
 			const struct gprs_rlcmac_pdch *pdch = &trx->pdch[ts_no];
 
-			if (pdch->m_is_enabled)
+			if (pdch_is_enabled(pdch))
 				num_pdch += 1;
 		}
 	}