power: qpnp-qg: Fix the return value

The return value should be 0 on success, however
the iio read reports 1 on success, ignore this
by reporting 0 on success from qg_battery_temp.

Change-Id: Ibdf0015870ebf56cb4565d1a8a342b8f998c68ba
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>