staging: greybus: Replaces directive __attribute__((packed)) by __packed as suggested by checkpatch

This patch makes the following changes:
 * Replaces '__attribute__((packed))' by '__packed' to remove warning as
   flagged by checkpatch

Signed-off-by: Jonathan Bergh <bergh.jonathan@gmail.com>
Link: https://lore.kernel.org/r/20240227160113.111264-2-bergh.jonathan@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>