power: smb5-lib: Use the unlocked version votable for FV

Float voltage is read in the batt_health() callback.
batt_health() is called from batt_status() and batt_status()
is also called from the FV callback leading to a deadlock.
Fix it by using the unlocked version of votable while reading FV.

Change-Id: Ie6f9f683c048a2a1c64d46716433bcff359dc3b0
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>