LoRaWAN: Fixed region 2(AU915) to compile

[AnttiKauppila]

ARM internal ref IOTCELL-948

Description

There was a typo in the code making it fail to compile

Pull request type

[x ] Fix
[ ] Refactor
[ ] New target
[ ] Feature
[ ] Breaking change

[AnttiKauppila]

This should go into next patch release 5.8.x

[0xc0170]

How come this was not catch in any of our CI?

cc @OPpuolitaival

[kivaisan]

@kjbracey-arm please review

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 1961
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6829/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Test : SUCCESS

Build number : 1776
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6829/1776

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1611
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6829/

[adbridge]

Manually cherry picked to 5.8.5