mwifiex: add unregister_dev handler for usb interface

Clear the data pointer stored in USB interface structure in
this handler. This helps to return from mwifiex_usb_disconnect()
if driver deinitialization is already performed while handling
an error path for mwifiex_usb_probe().

USB8797 card gets enumerated twice. First enumeration is for
firmware download and second enumeration expects firmware
initialization. mwifiex_usb_probe() always takes care of
deinitialization for first enumeration after firmware download.

Also, this change matches our handling for SDIO and PCIe
interfaces.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/mwifiex/usb.c

@@ -786,6 +786,13 @@ static int mwifiex_register_dev(struct mwifiex_adapter *adapter)
 	return 0;
 }
 
+static void mwifiex_unregister_dev(struct mwifiex_adapter *adapter)
+{
+	struct usb_card_rec *card = (struct usb_card_rec *)adapter->card;
+
+	usb_set_intfdata(card->intf, NULL);
+}
+
 static int mwifiex_prog_fw_w_helper(struct mwifiex_adapter *adapter,
 				    struct mwifiex_fw_image *fw)
 {
@@ -978,6 +985,7 @@ static int mwifiex_pm_wakeup_card(struct mwifiex_adapter *adapter)
 
 static struct mwifiex_if_ops usb_ops = {
 	.register_dev =		mwifiex_register_dev,
+	.unregister_dev =	mwifiex_unregister_dev,
 	.wakeup =		mwifiex_pm_wakeup_card,
 	.wakeup_complete =	mwifiex_pm_wakeup_card_complete,