power: qpnp-charger: fix vin_min for values > 5.6V

The set and get functions are incorrect for values
higher than 5.6V.

Fix this by correcting the calculations of VIN_MIN.

Change-Id: I32bb482db5425eedb30efc2d19a23981767b72d8
Signed-off-by: David Keitel <dkeitel@codeaurora.org>