platform/chrome: cros_ec_debugfs: cros_ec_uptime_fops can be static

Fixes: 909447f683b3 ("platform/chrome: cros_ec_debugfs: Add debugfs entry to retrieve EC uptime")
Signed-off-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>