Fix correct definition of sources for spi_flash component (GIT8266O-880)

[desertkun]

Description

components/spi_flash/CMakeLists.txt currently includes non-existent "src/partition" which should be "src/partition.c"

Related

Testing

On Latest CMake with policy -DCMAKE_POLICY_DEFAULT_CMP0115=NEW current project will not build.

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Checklist

Before submitting a Pull Request, please ensure the following:

• 🚨 This PR does not introduce breaking changes.
• All CI checks (GH Actions) pass.
• Documentation is updated as needed.
• Tests are updated or added as necessary.
• Code is well-commented, especially in complex areas.
• Git history is clean — commits are squashed to the minimum necessary.

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