power: supply: bq27xxx: Move health reading out of update loop

Most of the functions that read values return a status and put the value
itself in an a function parameter. Update health reading to match.

As health is not checked for changes as part of the update loop, remove
the read of this from the periodic update loop. This saves I2C/1W
bandwidth. It also means we do not have to cache it, fresh values are
read when requested.

Signed-off-by: Andrew Davis <afd@ti.com>
Link: https://lore.kernel.org/r/20240325203129.150030-6-afd@ti.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>