drivers: thermal: tsens: Add __func__ identifier to debug statements

Printing the function name when enabling debugging makes logs easier to
read.

Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/18717de35f31098d3ebc12564c2767b6d54d37d8.1572526427.git.amit.kucheria@linaro.org