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 <[e-mail]>
Signed-off-by: Zou Wei <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Hans de Goede <[e-mail]>

drivers/platform/x86/dell-wmi-sysman/sysman.c

···
 	return ret;
 }
 
-const struct sysfs_ops wmi_sysman_kobj_sysfs_ops = {
+static const struct sysfs_ops wmi_sysman_kobj_sysfs_ops = {
 	.show	= wmi_sysman_attr_show,
 	.store	= wmi_sysman_attr_store,
 };