Input: applespi - fix warnings detected by sparse

This makes sure that we convert from on-wire to CPU endianness in
applespi_debug_update_dimensions() and also marks as "static" as it is not
needed to be visible outside of the driver.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Ronald Tschalär <ronald@innovation.ch>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>