Input: usbtouchscreen - find input endpoint automatically

Find input enpoint automatically instead of assuming that the first one is
OK.  This is needed for devices with multiple endpoints such as iNexio
where the first endpoint might be output.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>