qcacld-3.0: Fix -Wmissing-prototypes in wlan_hdd_scan

We want to enable the compiler's -Wmissing-prototypes switch, but
there is existing code that is generating warnings. Fix all warnings
in wlan_hdd_scan.

Change-Id: I877d7e7b7be30a9195daad63d09999bb87f4add4
CRs-Fixed: 1074336

core/hdd/src/wlan_hdd_scan.c

@@ -598,7 +598,7 @@ static int wlan_hdd_scan_request_enqueue(hdd_adapter_t *adapter,
  *
  * Return: QDF_STATUS
  */
-QDF_STATUS wlan_hdd_scan_request_dequeue(hdd_context_t *hdd_ctx,
+static QDF_STATUS wlan_hdd_scan_request_dequeue(hdd_context_t *hdd_ctx,
 	uint32_t scan_id, struct cfg80211_scan_request **req, uint8_t *source,
 	uint32_t *timestamp)
 {