STM32L4 : code cleanup in MSI SetSysClock

[jeromecoutant]

Description

This follow #7647 discussion

For STM32L4 familly, clock configuration can use MSI (multispeed internal RC oscillator clock).
When a 32.768 kHz external oscillator (LSE) is present, it is possible to configure the MSI in a PLL-mode.
When configured in PLL-mode, the MSI automatically calibrates itself thanks to the LSE.

This setting was set 2 times during MSI configuration and even if LSE is not present.

@mattbrown015

Pull request type

[x] Fix
[ ] Refactor
[ ] Target update
[ ] Feature
[ ] Breaking change

[LMESTM]

Looks good to me - has this been tested ok on boards with LSE ?

[jeromecoutant]

/morph build

[cmonr]

@jeromecoutant Fyi, I stopped your build command. Maintainers are the only ones allowed to start builds due to how resource intensive those jobs are, especially when getting PRs ready during release periods.

[0xc0170]

We are now progressing with needs: CI PR, this will be restarted.

[0xc0170]

/morph build

[mbed-ci]

Build : FAILURE

Build number : 3013
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7787/

[cmonr]

[DEBUG] Output: Fatal error: A1023E: File "/tmp/file1QOyif" could not be opened: No such file or directory

Weird. @ARMmbed/mbed-os-test FYI^^^

/morph build

[cmonr]

Sorry, stopping the restart. Prioritizing PRs going into 5.10-rc2 and 5.9.7.

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 3049
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7787/

Triggering tests

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

[mbed-ci]

Test : SUCCESS

Build number : 2824
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7787/2824

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2666
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7787/