thermal: Spelling s/scallbacks/callbacks/

Fix a misspelling of the word "callbacks".

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/ae38372996a23bb67769e2d62ca170ae9457c4df.1626261946.git.geert+renesas@glider.be