thermal/drivers/mediatek/lvts_thermal: Use offsets for every calibration byte

Current code assumes calibration values are always stored contiguously
in host endian order. A future patch will prove this wrong.

Let's specify the offset for each calibration byte instead.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20240402032729.2736685-5-nico@fluxnic.net