power: qpnp-smb2: Add VOLTAGE_MAX_DESIGN property to usb power_supply

Modify existing VOLTAGE_MAX property of USB power_supply class to
reflect maximum voltage attainable by the current adapter settings.
Add VOLTAGE_MAX_DESIGN property to USB power_supply class to reflect
maximum voltage supported by PMIC.

Change-Id: Ia53b0993f1fa8735843894db40fb5c02bb9a5b17
Signed-off-by: Umang Agrawal <uagrawal@codeaurora.org>