ACPI: thermal: Drop some redundant code

Drop some redundant initialization of local variables, a redundant
return statement and a redundant "else" from the ACPI thermal driver.

No functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>