input: sensors: avoid accessing i2c bus when apds9930 is powered off

There's an observed issue that accessing i2c bus can cause kernel
crash when the sensor is powered off. Thus add some logic to avoid
accessing i2c bus before power off the sensor.

Change-Id: I604574ac3f4a9560daaec1b88ef7198d58b6f3db
Signed-off-by: Oliver Wang <mengmeng@codeaurora.org>