platform/x86: lenovo-yoga-tab2-pro-1380-fastcharger: Make symbol static

platform/x86: lenovo-yoga-tab2-pro-1380-fastcharger: Make symbol static

Sparse reports:

lenovo-yoga-tab2-pro-1380-fastcharger.c:222:29: warning: symbol
'yt2_1380_fc_serdev_driver' was not declared. Should it be static?

Fix that by making the symbol static.

Fixes: b2ed33e8d486a ("platform/x86: Add  lenovo-yoga-tab2-pro-1380-fastcharger driver")
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20250304160639.4295-1-ilpo.jarvinen@linux.intel.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>