This fixes maybe_unused warnings/errors.
According to a comment during device tree removal, only ACPI is supported,
thus let's actually require it.
Fixes: be18c5ede2 ("i2c: mlxbf: remove device tree support")
Signed-off-by: Adam Borowski <kilobyte@angband.pl>
Signed-off-by: Wolfram Sang <wsa@kernel.org>