qcacld-3.0: Fix buffer overflow when save chan tx power

Before copy tx power, need check length correctly to avoid
buffer overflow.

Change-Id: Ib18feaa36d3cbdcc50442885fd8b98888f34eab8
CRs-Fixed: 2538397

core/sme/src/csr/csr_api_scan.c

@@ -1557,7 +1557,7 @@ static void csr_save_tx_power_to_cfg(struct mac_context *mac,
 				count++;
 			}
 		} else {
-			if (cbLen >= dataLen) {
+			if (cbLen + sizeof(tSirMacChanInfo) >= dataLen) {
 				/* this entry will overflow our allocation */
 				sme_err(
 					"Buffer overflow, start freq %d, num %d, offset %d",