Input: cyttsp5 - fix array length

Input: cyttsp5 - fix array length

The cmd array should be initialized with the proper command size and not
with the actual command value that is sent to the touchscreen.

Signed-off-by: Maximilian Weigand <mweigand@mweigand.net>
Reviewed-by: Alistair Francis <alistair@alistair23.me>
Link: https://lore.kernel.org/r/20230501113010.891786-2-mweigand@mweigand.net
Fixes: 5b0c03e24a06 ("Input: Add driver for Cypress Generation 5 touchscreen")
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>