mfd: Tidy Kconfig dependency's parentheses

Drop unneeded parentheses for clarity and consistency.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Link: https://lore.kernel.org/r/20240407112445.503bcbc6@endymion.delvare


Signed-off-by: Lee Jones <lee@kernel.org>