carl9170: interrupt urbs must not set URB_ZERO_PACKET

This patch fixes a bug in the driver which was
exposed by CONFIG_USB_DEBUG:
	"usb 1-1.6.3: BOGUS urb flags, 40 --> 0"

The transfer flag "URB_ZERO_PACKET" is only valid
for bulk urbs.

Reported-by: André Erdmann
Signed-off-by: NChristian Lamparter <chunkeey@googlemail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/carl9170/usb.c

@@ -606,8 +606,6 @@ int __carl9170_exec_cmd(struct ar9170 *ar, struct carl9170_cmd *cmd,
 		AR9170_USB_EP_CMD), cmd, cmd->hdr.len + 4,
 		carl9170_usb_cmd_complete, ar, 1);
 
-	urb->transfer_flags |= URB_ZERO_PACKET;
-
 	if (free_buf)
 		urb->transfer_flags |= URB_FREE_BUFFER;