platform/chrome: lightbar: Use flexible array member

platform/chrome: lightbar: Use flexible array member

Variable arrays should be defined as [], not [0], otherwise
the kernel complains:

memcpy  : detected field-spanning write (size 9) of single field "param->set_program_ex.data" at drivers/platform/chrome/cros_ec_lightbar.c:603 (size 0)

Fixes: 9600b8bdbfe4 ("platform/chrome: lightbar: Add support for large sequence")
Signed-off-by: Gwendal Grignou <gwendal@google.com>
Link: https://lore.kernel.org/r/20260204034848.697033-1-gwendal@google.com
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>