Fix initialization order for I2CEEBlockDevice

[boomer41]

Summary of changes

Fix initialization order warning introduced in #12446

Impact of changes

Compiler warning won't be generated anymore (Tested with GCC_ARM)

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

[ciarmcom]

@boomer41, thank you for your changes.
@ARMmbed/mbed-os-storage @ARMmbed/mbed-os-maintainers please review.

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 8 of 8 test jobs passed
Build number : 1
Build artifacts