hwmon: (gsc-hwmon) Switch to flexible array to simplify code

Using flexible array is more straight forward. It
  - saves 1 pointer in the 'gsc_hwmon_platform_data' structure
  - saves an indirection when using this array
  - saves some LoC and avoids some always spurious pointer arithmetic

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/61a23e1d642397cfcecc4ac3bb0ab485d257987d.1668936855.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Guenter Roeck <linux@roeck-us.net>