MCS: use value_string for conversion

Change-Id: I212ebb892ab162821633974d5a6c7e315d308370
diff --git a/src/encoding.cpp b/src/encoding.cpp
index 58df95f..ad53b0b 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -1227,7 +1227,7 @@
 	default:
 		LOGP(DRLCMACDL, LOGL_ERROR,
 			"Encoding of uplink %s data blocks not yet supported.\n",
-			cs.name());
+			mcs_name(cs));
 		return -ENOTSUP;
 	};
 
@@ -1616,7 +1616,7 @@
 			count_payload);
 
 	LOGP(DRLCMACDL, LOGL_ERROR, "%s data block encoding not implemented\n",
-		cs.name());
+		mcs_name(cs));
 
 	return AR_NEED_MORE_BLOCKS;
 }