net: openthread: Fix missed logging macro usage

During recent upmerge OPENTHREAD_CONFIG_PLAT_LOG_FUNCTION__COUNT_ARGS
macro was renamed to OPENTHREAD_CONFIG_PLAT_LOG_MACRO_NAME__COUNT_ARGS
but the code wasn't updated where the macro is actually used.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>