Input: xpad - validate USB endpoint type during probe

We should only see devices with interrupt endpoints. Ignore any other
endpoints that we find, so we don't send try to send them interrupt URBs
and trigger a WARN down in the USB stack.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Cc: <stable@vger.kernel.org> # c01b5e74 Input: xpad - don't depend on endpoint order
Signed-off-by: Cameron Gutman <aicommander@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>