media: flexcop-usb: sanity checking of endpoint type

Make sure the endpoint is ISOC in and do not hard code USB_DIR_IN.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>