platform/x86/dell-wmi-sysman: Make wmi_sysman_kobj_sysfs_ops static

platform/x86/dell-wmi-sysman: Make wmi_sysman_kobj_sysfs_ops static

Fix the following sparse warning:

drivers/platform/x86/dell-wmi-sysman/sysman.c:258:24: warning:
symbol 'wmi_sysman_kobj_sysfs_ops' was not declared.
Should it be static?

wmi_sysman_kobj_sysfs_ops has only call within sysman.c
It should be static

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Link: https://lore.kernel.org/r/1603971581-64135-1-git-send-email-zou_wei@huawei.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>