thermal/drivers/k3_bandgap: Remove some unused fields in struct k3_bandgap

In "struct k3_bandgap", the 'conf' field is unused.
Remove it.

Found with cppcheck, unusedStructMember.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/206d39bed9ec6df9b4d80b1fc064e499389fc7fc.1712687420.git.christophe.jaillet@wanadoo.fr