lp8727_charger: Return if the battery is discharging

If the charger is pulled out, just return as DISCHARGING. Then no need for
additional 'else' statement.

Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>