input: sensors: change sensors classdev device's parent to input devices

Sensor HAL takes long time to scan /dev/input to get information
from input subsystem. Change the sensors sysfs hierachy to avoid
the scanning to reduce sensor HAL initialization time.

Change-Id: I6c89067eb8c3dfe5d97be6162639f0974a8a943f
Signed-off-by: Oliver Wang <mengmeng@codeaurora.org>