alloc: Simplify the assignment of Trb and Ttb

Put the cases for MS_A/MS_B and MS_A/MS_C together.
diff --git a/src/gprs_rlcmac_ts_alloc.cpp b/src/gprs_rlcmac_ts_alloc.cpp
index f48d8d4..b8028aa 100644
--- a/src/gprs_rlcmac_ts_alloc.cpp
+++ b/src/gprs_rlcmac_ts_alloc.cpp
@@ -236,13 +236,9 @@
 	Type = ms_class->type;
 
 	/* Tta and Ttb may depend on hopping or frequency change */
-	if (Ttb == MS_A)
+	if (Ttb == MS_A || Ttb == MS_B)
 		Ttb = 0;
-	if (Trb == MS_A)
-		Trb = 0;
-	if (Ttb == MS_B)
-		Ttb = 0;
-	if (Trb == MS_C)
+	if (Trb == MS_A || Trb == MS_C)
 		Trb = 0;
 
 	LOGP(DRLCMAC, LOGL_DEBUG, "- Rx=%d Tx=%d Sum Rx+Tx=%s  Tta=%s Ttb=%d "