power: supply: smb5: Properly opt-out from s/w based health reporting

Since we're either using bq2597x or ln8000, get_prop will always throw a
POWER_SUPPLY_HEALTH_UNKNOWN and then power_supply_show_property log it
as failed to report.
Instead of reporting unknown health and spamming log buffer, tell
userspace that there's no data for it.

Change-Id: Iebd346dfb235b132802d0f43956cd3d361d91c42
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>