thermal: exynos: Modify private_data to appropriate name driver_data

This patch renames member private_data to driver_data of the thermal
zone registration structure as this item stores the driver related
data and uses it to call the driver related callbacks.

Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Acked-by: Jonghwa Lee <jonghwa3.lee@samsung.com>
Acked-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>