processor: replace tab with white space

[nokute78]

This patch is to replace tab for readability.
https://github.com/fluent/fluent-bit/blob/master/CONTRIBUTING.md#coding-style

You have to pay attention to the code indentation, tabs are 4 spaces, spaces on conditionals, etc. If your code submission is not aligned, it will be rejected.

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Testing
Before we can approve your change; please submit the following in a comment:

• [N/A] Example configuration file for the change
• [N/A] Debug log output from testing the change

• [N/A] Attached Valgrind output that shows no leaks or memory corruption was found

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• [N/A] Run local packaging test showing all targets (including any new ones) build.
• [N/A] Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• [N/A] Documentation required for this feature

Backporting

• [N/A] Backport to latest stable release.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.