trats/trats2: exynos_power_init: return 0 if no battery detected.

trats/trats2: exynos_power_init: return 0 if no battery detected.

Generic board support is now enabled for Exynos 4, and if any
init function returns an error then the init process is stopped.

This makes a boot issue on the Trats and Trats2 devices. If the device
is supplied by USB cable or an external power supply then it can't boot
because function exynos_power_init returns an error. Now this function
returns 0 if battery is not connected.

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Cc: Piotr Wilczek <p.wilczek@samsung.com>
Cc: Minkyu Kang <mk7.kang@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>