pcu_l1_if.cpp: Drop unneeded byte in Imm Ass PCH buffer

paging group is 3 bytes and imm assign with plen prepended is 23 bytes,
so there's 1 extra byte not needed and makes code confusing.

Change-Id: Id7835e5aa1506505ff54e019b38f30111f79b5dc

src/pcu_l1_if.cpp

@@ -223,7 +223,7 @@ void pcu_l1if_tx_agch(bitvec * block, int plen)
 void pcu_l1if_tx_pch(bitvec * block, int plen, const char *imsi)
 {
 	struct gprs_rlcmac_bts *bts = bts_main_data();
-	uint8_t data[3+1+23]; /* prefix PLEN */
+	uint8_t data[3+23]; /* paging group, prefix PLEN */
 
 	/* paging group */
 	if (!imsi || strlen(imsi) < 3)