Input: edt-ft5x06 - calculate points data length only once

Input: edt-ft5x06 - calculate points data length only once

It is pointless and expensive to calculate data in the interrupt that
depends on the type of touchscreen, which is detected on the driver
probe and cannot then be changed.
So calculate the size of the data buffer on the driver probe, as well as
the data retrieval command, and then use them in the ISR.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Link: https://lore.kernel.org/r/20230402200951.1032513-10-dario.binacchi@amarulasolutions.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>