platform/mellanox: Add static in struct declaration.

Fix problem of missing static in struct declaration.

Fixes: 662f2482

 ("platform/mellanox: Add support for new SN2201 system")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Michael Shych <michaelsh@nvidia.com>
Link: https://lore.kernel.org/r/20220602145103.11859-1-michaelsh@nvidia.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>