power: smb5-lib: Fix wireless property in reading wireless VOUT

Power supply property POWER_SUPPLY_PROP_VOLTAGE_MAX is misused in getting
the current wireless output voltage from wireless psy. Replace it with
POWER_SUPPLY_PROP_INPUT_VOLTAGE_REGULATION.

Change-Id: Ibfb6c5b578fcc13e6c11e42c2d17e49ce9f19318
Signed-off-by: Harry Yang <harryy@codeaurora.org>