drivers: modem: rote conversion of k_work API

Replace all existing deprecated API with the recommended alternative.

Be aware that this does not address architectural errors in the use
of the work API.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
5 files changed