media: flexcop-usb: clean up endpoint sanity checks

Add a temporary variable to make the endpoint sanity checks a bit more
readable.

While at it, fix a typo in the usb_set_interface() comment.

Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20220822151456.27178-2-johan@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>