Add Description for tmp102 temperature sensor.

Cc: Felipe Balbi <balbi@ti.com>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Benoit Cousson <b-cousson@ti.com>