usb: wusbcore: set pointers to NULL after freeing in error cases

This patch fixes two cases where error handling code was freeing memory
but not setting the pointer to NULL.  This could lead to a double free
in the HWA shutdown code.
Signed-off-by: Thomas Pugliese <thomas.pugliese@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/wusbcore/wa-xfer.c

@@ -1560,6 +1560,7 @@ static void wa_xfer_result_chew(struct wahc *wa, struct wa_xfer *xfer,
 			xfer, seg_idx, result);
 	seg->result = result;
 	kfree(wa->buf_in_urb->sg);
+	wa->buf_in_urb->sg = NULL;
 error_sg_alloc:
 	__wa_xfer_abort(xfer);
 error_complete:
@@ -1859,6 +1860,7 @@ void wa_handle_notif_xfer(struct wahc *wa, struct wa_notif_hdr *notif_hdr)
 
 error_dti_urb_submit:
 	usb_put_urb(wa->buf_in_urb);
+	wa->buf_in_urb = NULL;
 error_buf_in_urb_alloc:
 	usb_put_urb(wa->dti_urb);
 	wa->dti_urb = NULL;