power: supply: adp5061: Fix a couple off by ones

We end up reading one element beyond the end of the adp5061_vmax[] array
here.

Fixes: fe8e81b7 ("adp5061: New driver for ADP5061 I2C battery charger")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>