mfd: twl4030-power: Fix poweroff with PM configuration enabled

Commit e7cd1d1e ("mfd: twl4030-power: Add generic reset
configuration") enabled configuring the PM features for twl4030.

This caused poweroff command to fail on devices that have the
BCI charger on twl4030 wired, or have power wired for VBUS.
Instead of powering off, the device reboots. This is because
voltage is detected on charger or VBUS with the default bits
enabled for the power transition registers.

To fix the issue, let's just clear VBUS and CHG bits as we want
poweroff command to keep the system powered off.

Fixes: e7cd1d1e ("mfd: twl4030-power: Add generic reset configuration")
Cc: stable@vger.kernel.org # v3.16+
Reported-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>