Input: ads7846 - set input device bus type and product ID

Set input device's bus type as BUS_SPI and use model as product ID.

Link: https://lore.kernel.org/r/20210910045039.4020199-1-dmitry.torokhov@gmail.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>