media: iguanair: fix endpoint sanity check

Make sure to use the current alternate setting, which need not be the
first one by index, when verifying the endpoint descriptors and
initialising the URBs.

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: 26ff6313 ("[media] Add support for the IguanaWorks USB IR Transceiver")
Fixes: ab1cbdf1 ("media: iguanair: add sanity checks")
Cc: stable <stable@vger.kernel.org>     # 3.6
Cc: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>