refactor: reduce the number of returns in superfluid migration (backport #6014)

[mergify]

This is an automatic backport of pull request #6014 done by Mergify.
Cherry-pick of 7a92e78 has failed:

On branch mergify/bp/v16.x/pr-6014
Your branch is up to date with 'origin/v16.x'.

You are currently cherry-picking commit 7a92e782.
  (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:   CHANGELOG.md
	modified:   x/gamm/keeper/migrate_test.go
	modified:   x/superfluid/keeper/migrate_test.go
	modified:   x/superfluid/keeper/msg_server.go
	modified:   x/superfluid/types/expected_keepers.go
	new file:   x/superfluid/types/migration.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   x/gamm/keeper/migrate.go
	both modified:   x/superfluid/keeper/export_test.go
	both modified:   x/superfluid/keeper/migrate.go

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

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