[feature-wisun] targets:RT1050: Fix the low speed switch issue

[liugang-gavin]

Fix the low speed switch issue when using QSPI flash

Signed-off-by: Tim Wang [email protected]

Summary of changes

The default clock and DLL adjustments are for HyperFlash，for NorFlash we should skip the configurations.

Impact of changes

No

Migration actions required

No

Documentation

No

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)

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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

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Reviewers

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[ciarmcom]

@liugang-gavin, thank you for your changes.
@ARMmbed/mbed-os-maintainers please review.

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 10 of 10 test jobs passed
Build number : 1
Build artifacts