thermal: imx: Use better parameter names than "val"

The values passed to imx_init_calib() and imx_init_temp_grade() are
read from specific OCOTP values. Use their names (in lower case) as
parameter name instead of "val" to make the code easier to understand.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>