power: supply: Provide stubs for charge_behaviour helpers

When CONFIG_SYSFS is not enabled provide stubs for the helper functions
to not break their callers.

Fixes: 539b9c94 ("power: supply: add helpers for charge_behaviour sysfs")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20220108153158.189489-1-linux@weissschuh.net


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