thermal/drivers/mediatek/lvts_thermal: Retrieve all calibration bytes

Calibration values are 24-bit wide. Those values so far appear to span
only 16 bits but let's not push our luck.

Found while looking at the original Mediatek driver code.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20240402032729.2736685-2-nico@fluxnic.net