This fixes the following warning when building with clang:

drivers/iio/light/isl29018.c:808:36: error: variable
    'isl29018_acpi_match' is not needed and will not be emitted
    [-Werror,-Wunneeded-internal-declaration]
Signed-off-by: NMatthias Kaehlcke <mka@chromium.org>
Reviewed-by: NGuenter Roeck <groeck@chromium.org>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>