EFM32: fix mbed_hal-pinmap test

[amq]

Summary of changes

Fixes #12371

Documentation

None.

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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)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[x] Tests / results supplied as part of this PR

mbed test --run -t GCC_ARM -m EFM32PG12_STK3402 -DMBED_EXTENDED_TESTS=1 -n tests-mbed_hal-pinmap -v

mbedgt: test suite report:
| target                    | platform_name     | test suite            | result | elapsed_time (sec) | copy_method |
|---------------------------|-------------------|-----------------------|--------|--------------------|-------------|
| EFM32PG12_STK3402-GCC_ARM | EFM32PG12_STK3402 | tests-mbed_hal-pinmap | OK     | 12.7               | default     |
mbedgt: test suite results: 1 OK
mbedgt: test case report:
| target                    | platform_name     | test suite            | test case           | passed | failed | result | elapsed_time (sec) |
|---------------------------|-------------------|-----------------------|---------------------|--------|--------|--------|--------------------|
| EFM32PG12_STK3402-GCC_ARM | EFM32PG12_STK3402 | tests-mbed_hal-pinmap | pinmap - validation | 1      | 0      | OK     | 0.08               |
mbedgt: test case results: 1 OK
mbedgt: completed in 13.04 sec

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Reviewers

@stevew817

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[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 1
Build artifacts