fix: event emission in erc20 precompile (backport #774)

[mergify]

no longer shadow the variable so we emit the proper amount in events

must be backported to v0.5.0

---

This is an automatic backport of pull request #774 done by Mergify.

[mergify]

Cherry-pick of a3a2a06 has failed:

On branch mergify/bp/release/v0.5.x/pr-774
Your branch is up to date with 'origin/release/v0.5.x'.

You are currently cherry-picking commit a3a2a06.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   precompiles/erc20/tx.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally