platform/x86/dell-wmi-sysman: Make some symbols static

Fix the following sparse warnings:

./passobj-attributes.c:38:23: warning: symbol 'po_is_pass_set' was not declared. Should it be static?
./passobj-attributes.c:70:23: warning: symbol 'po_current_password' was not declared. Should it be static?
./passobj-attributes.c:99:23: warning: symbol 'po_new_password' was not declared. Should it be static?
./passobj-attributes.c:103:23: warning: symbol 'po_min_pass_length' was not declared. Should it be static?
./passobj-attributes.c:107:23: warning: symbol 'po_max_pass_length' was not declared. Should it be static?
./passobj-attributes.c:116:23: warning: symbol 'po_mechanism' was not declared. Should it be static?
./passobj-attributes.c:129:23: warning: symbol 'po_role' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Link: https://lore.kernel.org/r/1604107922-14950-1-git-send-email-zou_wei@huawei.com


Signed-off-by: Hans de Goede <hdegoede@redhat.com>