Samsung: uart fixes

[heuisam]

Summary of changes

This commit fix bug, typo, and stdio uart port change from uart0 to uart2.

Bug fix

• fix uart1,2 baud-rate setting error
  When you tried to change the baud rate of uart1 or 2, the baud rate value was set to the uart0 register.
• Fix some typo.

Changes STDIO UART

• The stdio uart port changes from uart0 to uart2 as s1sbp6a devkit modified.

Impact of changes

Migration actions required

Documentation

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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]

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

[0xc0170]

CI started

[mbed-ci]

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jenkins-ci/mbed-os-ci_greentea-test	✔️
jenkins-ci/mbed-os-ci_cloud-client-pytest	✔️