chaneg log index to the index in block

[yihuang]

Closes #334

Description

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #354 (d0509a7) into main (2828fa1) will increase coverage by 0.13%.
The diff coverage is 93.33%.

@@            Coverage Diff             @@
##             main     #354      +/-   ##
==========================================
+ Coverage   52.47%   52.60%   +0.13%     
==========================================
  Files          46       46              
  Lines        4606     4619      +13     
==========================================
+ Hits         2417     2430      +13     
  Misses       2089     2089              
  Partials      100      100              

Impacted Files	Coverage Δ
x/evm/types/key.go	0.00% <ø> (ø)
x/evm/types/logs.go	36.47% <0.00%> (-0.44%)	⬇️
x/evm/keeper/keeper.go	69.46% <100.00%> (+2.79%)	⬆️
x/evm/keeper/statedb.go	84.65% <100.00%> (+0.03%)	⬆️

[fedekunze]

very clean PR. thanks!