drivers: thermal: tsens: use simpler variables

We already dereference the sensor and save it into a variable. Use the
variable directly to make the code easier to read.

Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/5dc4356edfb8dffa377fb561359bf41a6f1fdf17.1584015867.git.amit.kucheria@linaro.org