staging: vt6655: device_rx_srv check sk_buff is NULL

commit b5eeed8c upstream.

There is a small chance that pRD->pRDInfo->skb could go NULL
while the interrupt is processing.

Put NULL check on loop to break out.
Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit 35ee488d)
Signed-off-by: Willy Tarreau <w@1wt.eu>

drivers/staging/vt6655/device_main.c

@@ -1605,6 +1605,10 @@ static int device_rx_srv(PSDevice pDevice, UINT uIdx) {
 //        DBG_PRT(MSG_LEVEL_DEBUG, KERN_INFO "pDevice->pCurrRD = %x, works = %d\n", pRD, works);
         if (works++>15)
             break;
+
+        if (!pRD->pRDInfo->skb)
+            break;
+
         if (device_receive_frame(pDevice, pRD)) {
             if (!device_alloc_rx_buf(pDevice,pRD)) {
                     DBG_PRT(MSG_LEVEL_ERR, KERN_ERR