mwifiex: pcie: tighten a check in mwifiex_pcie_process_event_ready()

If "evt_len" is 1 then we try to memcpy() negative 3 bytes and it would
cause memory corruption.

Fixes: d930faee ("mwifiex: add support for Marvell pcie8766 chipset")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/marvell/mwifiex/pcie.c

@@ -1881,7 +1881,8 @@ static int mwifiex_pcie_process_event_ready(struct mwifiex_adapter *adapter)
 		mwifiex_dbg(adapter, EVENT,
 			    "info: Event length: %d\n", evt_len);
 
-		if ((evt_len > 0) && (evt_len  < MAX_EVENT_SIZE))
+		if (evt_len > MWIFIEX_EVENT_HEADER_LEN &&
+		    evt_len < MAX_EVENT_SIZE)
 			memcpy(adapter->event_body, skb_cmd->data +
 			       MWIFIEX_EVENT_HEADER_LEN, evt_len -
 			       MWIFIEX_EVENT_HEADER_LEN);