drivers: thermal: tsens: Rename variable tmdev

tmdev seems to imply that this is a device pointer when in fact it is
just private platform data for each tsens device. Rename it to priv
improve code readability.

Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>