Lora: Fix LoRaMacCrypto asserts

[kivaisan]

Description

If Lora stack is built with incorrect mbedtls settings, crypto methods
should assert and return error value. This fixes MBED_ASSERTs to
work correctly.

This is a fix for issue #6764.

Pull request type

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

[kivaisan]

@hasnainvirk @kjbracey-arm @AnttiKauppila please review.

[hasnainvirk]

@kivaisan Can you please check why the CI became unstable ? @0xc0170 If its just CI not being available, can we re-run CI for this ?

[0xc0170]

jenkins CI - started failing yesterday afternoon, we are investigating the cause, might not be related to this changeset.

[0xc0170]

I restarted jenkins CI, should be green if all OK here. The CI issue was resolved.

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 1932
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6800/

Triggering tests

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

[mbed-ci]

Test : SUCCESS

Build number : 1754
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6800/1754

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1578
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6800/

[adbridge]

This fix is on top of #6692 which is targeted for 5.9.