drivers: modem: ublox-sara-r4: freeaddrinfo mark unused param

The res param in offload_freeaddrinfo is not used.
Mark it as unused, to avoid static analysis complaining about
Parse warning (PW.PARAM_SET_BUT_NOT_USED)
Fixes CID 316235

Signed-off-by: Thomas Stranger <thomas.stranger@outlook.com>