power: qpnp-charger: apply polarity change of ibat

Since the sign of battery CURRENT_NOW prop is opposite
of qpnp-charger's convention, apply ibat polarity change
for the charger driver.

Change-Id: Ib4221228e3297b889786dfb390eb14f21491593d
Signed-off-by: choongryeol.lee <choongryeol.lee@lge.com>