Input: goodix - fix variable length array warning

Fix sparse warning:

drivers/input/touchscreen/goodix.c:182:26: warning: Variable length array is used.

Replace the variable length array with fixed length.

Some Goodix devices have maximum 5 touch points, while others have 10 touch
points. Using the maximum length (80 bytes) for all devices will lead to
wasting 40 bytes on stack when using devices with maximum 5 touch points.
However, that is preferable to using kmalloc which will use even more
resources.

Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>
Acked-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>