qcacmn: Avoid NULL pointer dereference of pdev

Suspicious dereference of pointer 'pdev' by passing argument
to function 'dp_find_peer_by_addr' in dp_register_peer.

Add NULL check before dereference of pointer 'pdev'.

Change-Id: Ibe2db784287ff1557aec983829781378578016c0
CRs-Fixed: 2668253

dp/wifi3.0/dp_peer.c

@@ -3436,12 +3436,12 @@ QDF_STATUS dp_register_peer(struct cdp_soc_t *soc_hdl, uint8_t pdev_id,
 	struct dp_soc *soc = cdp_soc_t_to_dp_soc(soc_hdl);
 	struct dp_pdev *pdev = dp_get_pdev_from_soc_pdev_id_wifi3(soc, pdev_id);
 
-	peer = dp_find_peer_by_addr((struct cdp_pdev *)pdev,
-				    sta_desc->peer_addr.bytes);
-
 	if (!pdev)
 		return QDF_STATUS_E_FAULT;
 
+	peer = dp_find_peer_by_addr((struct cdp_pdev *)pdev,
+				    sta_desc->peer_addr.bytes);
+
 	if (!peer)
 		return QDF_STATUS_E_FAULT;