power: qpnp-qg: Update the error return value

The power-supply framework uses -ENODEV to identify a missing
battery, use the same in the Qgauge driver.

While at it, remove a couple of unnecessary error prints.

Change-Id: Ife1972a4d8e2bdbf482c7c1c7cb3a6f8461d5a45
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>