iio: temperature: mlx90632: Add missing static marking on devm_pm_ops

Only used within this file, so should be marked static.

Fixes: 2aebc223 ("iio: temperature: mlx90632 Add runtime powermanagement modes")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-off-by: Crt Mori <cmo@melexis.com>
Link: https://lore.kernel.org/r/20221105125108.383193-3-jic23@kernel.org