Add Description for tmp102 temperature sensor.

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