Memory leak fix in NFA_SetRfDiscoveryDuration()

Test: compile
Change-Id: Id896d79e09def5c978d1a95548a1fa231510f708

Author: JizhouLiao

src/nfa/dm/nfa_dm_api.c

@@ -738,7 +738,8 @@ tNFA_STATUS NFA_SetRfDiscoveryDuration(uint16_t discovery_period_ms) {
   NFA_TRACE_API0("NFA_SetRfDiscoveryDuration ()");
 
   /* Post the API message */
-  p_msg = (tNFA_DM_API_SET_RF_DISC_DUR*)GKI_getbuf(sizeof(NFC_HDR));
+  p_msg = (tNFA_DM_API_SET_RF_DISC_DUR*)GKI_getbuf(
+      sizeof(tNFA_DM_API_SET_RF_DISC_DUR));
   if (p_msg != NULL) {
     p_msg->hdr.event = NFA_DM_API_SET_RF_DISC_DURATION_EVT;