thermal: rcar_thermal: Add missing braces to conditional statement

According to Documentation/process/coding-style.rst, if one branch of a
conditional statement needs braces, both branches should use braces.

Fixes: bbcf90c0 ("thermal: Explicitly enable non-changing thermal zone devices")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200819092716.3191-1-geert+renesas@glider.be