staging: rtl8188eu: fix interface sanity check

Make sure to use the current alternate setting when verifying the
interface descriptors to avoid binding to an invalid interface.

Failing to do so could cause the driver to misbehave or trigger a WARN()
in usb_submit_urb() that kernels with panic_on_warn set would choke on.

Fixes: c2478d3 ("staging: r8188eu: Add files for new driver - part 20")
Cc: stable <stable@vger.kernel.org>     # 3.12
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191210114751.5119-2-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/os_dep/usb_intf.c

@@ -70,7 +70,7 @@ static struct dvobj_priv *usb_dvobj_init(struct usb_interface *usb_intf)
 	phost_conf = pusbd->actconfig;
 	pconf_desc = &phost_conf->desc;
 
-	phost_iface = &usb_intf->altsetting[0];
+	phost_iface = usb_intf->cur_altsetting;
 	piface_desc = &phost_iface->desc;
 
 	pdvobjpriv->NumInterfaces = pconf_desc->bNumInterfaces;