staging: rtl8712: fix interface sanity check

staging: rtl8712: fix interface sanity check

commit c724f776f048538ecfdf53a52b7a522309f5c504 upstream.

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: 2865d42c78a9 ("staging: r8712u: Add the new driver to the mainline kernel")
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191210114751.5119-3-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>