power: smb5-lib: Show unknown battery status for debug battery

For a debug battery (battery id is 7.5 K), show the battery
status as unknown instead of discharging/not charging. Since the
charging is disabled for debug battery, this makes sense. Also,
it helps the userspace to stay in poweron mode based on the user
request.

Change-Id: Ia83e2c3903a01c0f61e9cbbb5b05f30668f6d652
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>