STM32H7: FDCAN: use PLL1Q frequency for calculations

[facchinm]

Summary of changes

FDCAN baud calculation was wrong if the clock feeding the IP is not 10MHz.
While waiting for the ST HAL fix, since the feed is always PLL1.Q, use that value to propely calulate the baud rate.

Impact of changes

Migration actions required

Documentation

None

Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

---

Test results

[] No Tests required for this change (E.g docs only update)
[x] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

---

Reviewers

@jeromecoutant @manchoz

---

[ciarmcom]

@facchinm, thank you for your changes.
@jeromecoutant @ARMmbed/team-st-mcd @ARMmbed/mbed-os-maintainers please review.

[jeromecoutant]

Can't test, but I suppose you did!

[0xc0170]

CI started

[mbed-ci]

Jenkins CI Test : ✔️ SUCCESS

Build Number: 1 | 🔒 Jenkins CI Job | 🌐 Logs & Artifacts

CLICK for Detailed Summary

jobs	Status
jenkins-ci/mbed-os-ci_unittests	✔️
jenkins-ci/mbed-os-ci_cmake-example-GCC_ARM	✔️
jenkins-ci/mbed-os-ci_cmake-example-ARM	✔️
jenkins-ci/mbed-os-ci_build-greentea-ARM	✔️
jenkins-ci/mbed-os-ci_build-cloud-example-ARM	✔️
jenkins-ci/mbed-os-ci_build-cloud-example-GCC_ARM	✔️
jenkins-ci/mbed-os-ci_build-greentea-GCC_ARM	✔️
jenkins-ci/mbed-os-ci_build-example-ARM	✔️
jenkins-ci/mbed-os-ci_build-example-GCC_ARM	✔️
jenkins-ci/mbed-os-ci_greentea-test	✔️
jenkins-ci/mbed-os-ci_cmake-example-test	✔️